diff --git a/change-notes/2020-12-18-goproxy.md b/change-notes/2020-12-18-goproxy.md
new file mode 100644
index 00000000000..e56d542a76b
--- /dev/null
+++ b/change-notes/2020-12-18-goproxy.md
@@ -0,0 +1,5 @@
+lgtm,codescanning
+* Added support for the `github.com/elazarl/goproxy` package.
+* The query "Incomplete regular expression for hostnames" has been improved to recognize some cases
+  when the regexp in question is guarding an HTTP error response, which will lead to fewer false
+  positives.
diff --git a/ql/src/Security/CWE-020/IncompleteHostnameRegexp.ql b/ql/src/Security/CWE-020/IncompleteHostnameRegexp.ql
index 8aa7dae4c27..802f2cb61d5 100644
--- a/ql/src/Security/CWE-020/IncompleteHostnameRegexp.ql
+++ b/ql/src/Security/CWE-020/IncompleteHostnameRegexp.ql
@@ -30,6 +30,55 @@ predicate isIncompleteHostNameRegexpPattern(string pattern, string hostPart) {
             "(([():|?a-z0-9-]+(\\\\)?[.])?" + commonTLD() + ")" + ".*", 1)
 }
 
+/** Holds if `b` sets the HTTP status code (represented by a pseudo-header named  `status`) */
+predicate writesHttpError(ReachableBasicBlock b) {
+  forex(HTTP::HeaderWrite hw |
+    hw.getHeaderName() = "status" and hw.asInstruction().getBasicBlock() = b
+  |
+    exists(string code | code.matches("4__") or code.matches("5__") |
+      hw.definesHeader("status", code)
+    )
+  )
+}
+
+/** Holds if starting from `block` a status code representing an error is certainly set. */
+predicate onlyErrors(BasicBlock block) {
+  writesHttpError(block)
+  or
+  forex(ReachableBasicBlock pred | pred = block.getAPredecessor() | onlyErrors(pred))
+}
+
+/** Gets a node that refers to a handler that is considered to return an HTTP error. */
+DataFlow::Node getASafeHandler() {
+  exists(Variable v |
+    v.hasQualifiedName(ElazarlGoproxy::packagePath(), ["AlwaysReject", "RejectConnect"])
+  |
+    result = v.getARead()
+  )
+  or
+  exists(Function f |
+    onlyErrors(f.getFuncDecl().(ControlFlow::Root).getExitNode().getBasicBlock())
+  |
+    result = f.getARead()
+  )
+}
+
+/** Holds if `regexp` is used in a check before `handler` is called. */
+predicate regexpGuardsHandler(RegexpPattern regexp, HTTP::RequestHandler handler) {
+  handler.guardedBy(DataFlow::exprNode(regexp.getAUse().asExpr().getParent*()))
+}
+
+/** Holds if `regexp` guards an HTTP error write. */
+predicate regexpGuardsError(RegexpPattern regexp) {
+  exists(ControlFlow::ConditionGuardNode cond, RegexpMatchFunction match, DataFlow::CallNode call |
+    call.getTarget() = match and
+    match.getRegexp(call) = regexp
+  |
+    cond.ensures(match.getResult().getNode(call).getASuccessor*(), true) and
+    cond.dominates(any(ReachableBasicBlock b | writesHttpError(b)))
+  )
+}
+
 class Config extends DataFlow::Configuration {
   Config() { this = "IncompleteHostNameRegexp::Config" }
 
@@ -47,7 +96,13 @@ class Config extends DataFlow::Configuration {
 
   override predicate isSource(DataFlow::Node source) { isSource(source, _) }
 
-  override predicate isSink(DataFlow::Node sink) { sink instanceof RegexpPattern }
+  override predicate isSink(DataFlow::Node sink) {
+    sink instanceof RegexpPattern and
+    forall(HTTP::RequestHandler handler | regexpGuardsHandler(sink, handler) |
+      not handler = getASafeHandler()
+    ) and
+    not regexpGuardsError(sink)
+  }
 }
 
 from Config c, DataFlow::PathNode source, DataFlow::PathNode sink, string hostPart
diff --git a/ql/src/go.qll b/ql/src/go.qll
index 85f99b3c774..393858594c0 100644
--- a/ql/src/go.qll
+++ b/ql/src/go.qll
@@ -34,6 +34,7 @@ import semmle.go.frameworks.BeegoOrm
 import semmle.go.frameworks.Chi
 import semmle.go.frameworks.Couchbase
 import semmle.go.frameworks.Echo
+import semmle.go.frameworks.ElazarlGoproxy
 import semmle.go.frameworks.Email
 import semmle.go.frameworks.Encoding
 import semmle.go.frameworks.EvanphxJsonPatch
diff --git a/ql/src/semmle/go/concepts/HTTP.qll b/ql/src/semmle/go/concepts/HTTP.qll
index b4622b09515..3a5b9b8ff8b 100644
--- a/ql/src/semmle/go/concepts/HTTP.qll
+++ b/ql/src/semmle/go/concepts/HTTP.qll
@@ -64,10 +64,17 @@ module HTTP {
       /** Gets the (lower-case) name of a header set by this definition. */
       string getHeaderName() { result = this.getName().getStringValue().toLowerCase() }
 
+      /** Gets the value of the header set by this definition. */
+      string getHeaderValue() {
+        result = this.getValue().getStringValue()
+        or
+        result = this.getValue().getIntValue().toString()
+      }
+
       /** Holds if this header write defines the header `header`. */
       predicate definesHeader(string header, string value) {
         header = this.getHeaderName() and
-        value = this.getValue().getStringValue()
+        value = this.getHeaderValue()
       }
 
       /**
@@ -101,6 +108,9 @@ module HTTP {
     /** Gets the (lower-case) name of a header set by this definition. */
     string getHeaderName() { result = self.getHeaderName() }
 
+    /** Gets the value of the header set by this definition. */
+    string getHeaderValue() { result = self.getHeaderValue() }
+
     /** Holds if this header write defines the header `header`. */
     predicate definesHeader(string header, string value) { self.definesHeader(header, value) }
 
@@ -302,4 +312,33 @@ module HTTP {
     /** Gets the response writer that this redirect is sent on, if any. */
     ResponseWriter getResponseWriter() { result = self.getResponseWriter() }
   }
+
+  /** Provides a class for modeling new HTTP handler APIs. */
+  module RequestHandler {
+    /**
+     * An HTTP request handler.
+     *
+     * Extend this class to model new APIs. If you want to refine existing API models,
+     * extend `HTTP::RequestHandler` instead.
+     */
+    abstract class Range extends DataFlow::Node {
+      /** Gets a node that is used in a check that is tested before this handler is run. */
+      abstract predicate guardedBy(DataFlow::Node check);
+    }
+  }
+
+  /**
+   * An HTTP request handler.
+   *
+   * Extend this class to refine existing API models. If you want to model new APIs,
+   * extend `HTTP::RequestHandler::Range` instead.
+   */
+  class RequestHandler extends DataFlow::Node {
+    RequestHandler::Range self;
+
+    RequestHandler() { this = self }
+
+    /** Gets a node that is used in a check that is tested before this handler is run. */
+    predicate guardedBy(DataFlow::Node check) { self.guardedBy(check) }
+  }
 }
diff --git a/ql/src/semmle/go/frameworks/ElazarlGoproxy.qll b/ql/src/semmle/go/frameworks/ElazarlGoproxy.qll
new file mode 100644
index 00000000000..f6023ba12c7
--- /dev/null
+++ b/ql/src/semmle/go/frameworks/ElazarlGoproxy.qll
@@ -0,0 +1,135 @@
+/**
+ * Provides classes for working with concepts relating to the [github.com/elazarl/goproxy](https://pkg.go.dev/github.com/elazarl/goproxy) package.
+ */
+
+import go
+
+/**
+ * Provides classes for working with concepts relating to the [github.com/elazarl/goproxy](https://pkg.go.dev/github.com/elazarl/goproxy) package.
+ */
+module ElazarlGoproxy {
+  /** Gets the package name. */
+  bindingset[result]
+  string packagePath() { result = package("github.com/elazarl/goproxy", "") }
+
+  private class NewResponse extends HTTP::HeaderWrite::Range, DataFlow::CallNode {
+    NewResponse() { this.getTarget().hasQualifiedName(packagePath(), "NewResponse") }
+
+    override string getHeaderName() { this.definesHeader(result, _) }
+
+    override string getHeaderValue() { this.definesHeader(_, result) }
+
+    override DataFlow::Node getName() { none() }
+
+    override DataFlow::Node getValue() { result = this.getArgument([1, 2]) }
+
+    override predicate definesHeader(string header, string value) {
+      header = "status" and value = this.getArgument(2).getIntValue().toString()
+      or
+      header = "content-type" and value = this.getArgument(1).getStringValue()
+    }
+
+    override HTTP::ResponseWriter getResponseWriter() { none() }
+  }
+
+  /** A body argument to a `NewResponse` call. */
+  private class NewResponseBody extends HTTP::ResponseBody::Range {
+    NewResponse call;
+
+    NewResponseBody() { this = call.getArgument(3) }
+
+    override DataFlow::Node getAContentTypeNode() { result = call.getArgument(1) }
+
+    override HTTP::ResponseWriter getResponseWriter() { none() }
+  }
+
+  private class TextResponse extends HTTP::HeaderWrite::Range, DataFlow::CallNode {
+    TextResponse() { this.getTarget().hasQualifiedName(packagePath(), "TextResponse") }
+
+    override string getHeaderName() { this.definesHeader(result, _) }
+
+    override string getHeaderValue() { this.definesHeader(_, result) }
+
+    override DataFlow::Node getName() { none() }
+
+    override DataFlow::Node getValue() { none() }
+
+    override predicate definesHeader(string header, string value) {
+      header = "status" and value = "200"
+      or
+      header = "content-type" and value = "text/plain"
+    }
+
+    override HTTP::ResponseWriter getResponseWriter() { none() }
+  }
+
+  /** A body argument to a `TextResponse` call. */
+  private class TextResponseBody extends HTTP::ResponseBody::Range, TextResponse {
+    TextResponse call;
+
+    TextResponseBody() { this = call.getArgument(2) }
+
+    override DataFlow::Node getAContentTypeNode() { result = call.getArgument(1) }
+
+    override HTTP::ResponseWriter getResponseWriter() { none() }
+  }
+
+  /** A handler attached to a goproxy proxy type. */
+  private class ProxyHandler extends HTTP::RequestHandler::Range {
+    DataFlow::MethodCallNode handlerReg;
+
+    ProxyHandler() {
+      handlerReg
+          .getTarget()
+          .hasQualifiedName(packagePath(), "ReqProxyConds", ["Do", "DoFunc", "HandleConnect"]) and
+      this = handlerReg.getArgument(0)
+    }
+
+    override predicate guardedBy(DataFlow::Node check) {
+      // note OnResponse is not modeled, as that server responses are not currently considered untrusted input
+      exists(DataFlow::MethodCallNode onreqcall |
+        onreqcall.getTarget().hasQualifiedName(packagePath(), "ProxyHttpServer", "OnRequest")
+      |
+        handlerReg.getReceiver() = onreqcall.getASuccessor*() and
+        check = onreqcall.getArgument(0)
+      )
+    }
+  }
+
+  private class UserControlledRequestData extends UntrustedFlowSource::Range {
+    UserControlledRequestData() {
+      exists(DataFlow::FieldReadNode frn | this = frn |
+        // liberally consider ProxyCtx.UserData to be untrusted; it's a data field set by a request handler
+        frn.getField().hasQualifiedName(packagePath(), "ProxyCtx", "UserData")
+      )
+      or
+      exists(DataFlow::MethodCallNode call | this = call |
+        call.getTarget().hasQualifiedName(packagePath(), "ProxyCtx", "Charset")
+      )
+    }
+  }
+
+  private class ProxyLog extends LoggerCall::Range, DataFlow::MethodCallNode {
+    ProxyLog() { this.getTarget().hasQualifiedName(packagePath(), "ProxyCtx", ["Logf", "Warnf"]) }
+
+    override DataFlow::Node getAMessageComponent() { result = this.getAnArgument() }
+  }
+
+  private class MethodModels extends TaintTracking::FunctionModel, Method {
+    FunctionInput inp;
+    FunctionOutput outp;
+
+    MethodModels() {
+      // Methods:
+      // signature: func CertStorage.Fetch(hostname string, gen func() (*tls.Certificate, error)) (*tls.Certificate, error)
+      //
+      // `hostname` excluded because if the cert storage or generator function themselves have not
+      // been tainted, `hostname` would be unlikely to fetch user-controlled data
+      this.hasQualifiedName(packagePath(), "CertStorage", "Fetch") and
+      (inp.isReceiver() or inp.isParameter(1)) and
+      outp.isResult(0)
+    }
+
+    override predicate hasTaintFlow(FunctionInput i, FunctionOutput o) { i = inp and o = outp }
+  }
+}
diff --git a/ql/src/semmle/go/frameworks/stdlib/NetHttp.qll b/ql/src/semmle/go/frameworks/stdlib/NetHttp.qll
index 830e47f3c7e..575267c0f88 100644
--- a/ql/src/semmle/go/frameworks/stdlib/NetHttp.qll
+++ b/ql/src/semmle/go/frameworks/stdlib/NetHttp.qll
@@ -108,10 +108,6 @@ module NetHttp {
 
     override string getHeaderName() { result = "status" }
 
-    override predicate definesHeader(string header, string value) {
-      header = "status" and value = this.getValue().getIntValue().toString()
-    }
-
     override DataFlow::Node getName() { none() }
 
     override DataFlow::Node getValue() { result = this.getArgument(0) }
@@ -119,6 +115,18 @@ module NetHttp {
     override HTTP::ResponseWriter getResponseWriter() { result.getANode() = this.getReceiver() }
   }
 
+  private class ResponseErrorCall extends HTTP::HeaderWrite::Range, DataFlow::CallNode {
+    ResponseErrorCall() { this.getTarget().hasQualifiedName("net/http", "Error") }
+
+    override string getHeaderName() { result = "status" }
+
+    override DataFlow::Node getName() { none() }
+
+    override DataFlow::Node getValue() { result = this.getArgument(2) }
+
+    override HTTP::ResponseWriter getResponseWriter() { result.getANode() = this.getArgument(0) }
+  }
+
   private class RequestBody extends HTTP::RequestBody::Range, DataFlow::ExprNode {
     RequestBody() {
       exists(Function newRequest |
@@ -227,6 +235,20 @@ module NetHttp {
     }
   }
 
+  private class Handler extends HTTP::RequestHandler::Range {
+    DataFlow::CallNode handlerReg;
+
+    Handler() {
+      exists(Function regFn | regFn = handlerReg.getTarget() |
+        regFn.hasQualifiedName("net/http", ["Handle", "HandleFunc"]) or
+        regFn.(Method).hasQualifiedName("net/http", "ServeMux", ["Handle", "HandleFunc"])
+      ) and
+      this = handlerReg.getArgument(1)
+    }
+
+    override predicate guardedBy(DataFlow::Node check) { check = handlerReg.getArgument(0) }
+  }
+
   private class FunctionModels extends TaintTracking::FunctionModel {
     FunctionInput inp;
     FunctionOutput outp;
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/Handler.expected b/ql/test/library-tests/semmle/go/concepts/HTTP/Handler.expected
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/Handler.ql b/ql/test/library-tests/semmle/go/concepts/HTTP/Handler.ql
new file mode 100644
index 00000000000..2ab16946cf9
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/Handler.ql
@@ -0,0 +1,18 @@
+import go
+import TestUtilities.InlineExpectationsTest
+
+class HttpHandler extends InlineExpectationsTest {
+  HttpHandler() { this = "httphandler" }
+
+  override string getARelevantTag() { result = "handler" }
+
+  override predicate hasActualResult(string file, int line, string element, string tag, string value) {
+    tag = "handler" and
+    exists(HTTP::RequestHandler h, DataFlow::Node check |
+      element = h.toString() and value = check.toString()
+    |
+      h.hasLocationInfo(file, line, _, _, _) and
+      h.guardedBy(check)
+    )
+  }
+}
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/Header.expected b/ql/test/library-tests/semmle/go/concepts/HTTP/Header.expected
index 1c57549d95b..e9d4558e705 100644
--- a/ql/test/library-tests/semmle/go/concepts/HTTP/Header.expected
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/Header.expected
@@ -1,10 +1,10 @@
-| main.go:29:2:29:19 | call to WriteHeader | n/a | 418 | status | 418 |
-| main.go:31:2:31:51 | call to Set | "Authorization" | "Basic example:example" | authorization | Basic example:example |
-| main.go:32:2:32:26 | call to Add | "Age" | "342232" | age | 342232 |
-| main.go:34:2:34:55 | call to Add | server | call to Sprintf | n/a | n/a |
-| main.go:35:2:35:45 | call to Set | LOC_HEADER | ...+... | n/a | n/a |
-| main.go:36:2:36:5 | head | "Unknown-Header" | slice literal | n/a | n/a |
-| main.go:48:2:48:43 | call to Add | "Not-A-Response" | "Header" | not-a-response | Header |
-| main.go:49:2:49:42 | call to Set | "Accept" | "nota/response" | accept | nota/response |
-| main.go:50:2:50:11 | selection of Header | "Accept-Charset" | slice literal | n/a | n/a |
-| main.go:57:2:57:42 | call to Set | "This-Makes" | "No sense" | this-makes | No sense |
+| main.go:30:2:30:19 | call to WriteHeader | n/a | 418 | status | 418 |
+| main.go:32:2:32:51 | call to Set | "Authorization" | "Basic example:example" | authorization | Basic example:example |
+| main.go:33:2:33:26 | call to Add | "Age" | "342232" | age | 342232 |
+| main.go:35:2:35:55 | call to Add | server | call to Sprintf | n/a | n/a |
+| main.go:36:2:36:45 | call to Set | LOC_HEADER | ...+... | n/a | n/a |
+| main.go:37:2:37:5 | head | "Unknown-Header" | slice literal | n/a | n/a |
+| main.go:49:2:49:43 | call to Add | "Not-A-Response" | "Header" | not-a-response | Header |
+| main.go:50:2:50:42 | call to Set | "Accept" | "nota/response" | accept | nota/response |
+| main.go:51:2:51:11 | selection of Header | "Accept-Charset" | slice literal | n/a | n/a |
+| main.go:58:2:58:42 | call to Set | "This-Makes" | "No sense" | this-makes | No sense |
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/RequestBody.expected b/ql/test/library-tests/semmle/go/concepts/HTTP/RequestBody.expected
index 1d2ac44dc6a..3a835aec7d6 100644
--- a/ql/test/library-tests/semmle/go/concepts/HTTP/RequestBody.expected
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/RequestBody.expected
@@ -1,2 +1,2 @@
-| main.go:46:57:46:59 | nil |
-| main.go:52:13:52:34 | call to NopCloser |
+| main.go:47:57:47:59 | nil |
+| main.go:53:13:53:34 | call to NopCloser |
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/ResponseBody.expected b/ql/test/library-tests/semmle/go/concepts/HTTP/ResponseBody.expected
index f36de03103b..7cba3845c39 100644
--- a/ql/test/library-tests/semmle/go/concepts/HTTP/ResponseBody.expected
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/ResponseBody.expected
@@ -1,2 +1,4 @@
-| main.go:38:10:38:40 | type conversion |
-| main.go:40:20:40:30 | "Body text" |
+| main.go:39:10:39:40 | type conversion |
+| main.go:41:20:41:30 | "Body text" |
+| main.go:63:18:63:28 | "Hello, %q" |
+| main.go:63:31:63:59 | call to EscapeString |
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/UntrustedFlowSources.expected b/ql/test/library-tests/semmle/go/concepts/HTTP/UntrustedFlowSources.expected
index f2f61551504..bf47ab17a58 100644
--- a/ql/test/library-tests/semmle/go/concepts/HTTP/UntrustedFlowSources.expected
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/UntrustedFlowSources.expected
@@ -1,14 +1,15 @@
-| main.go:16:10:16:15 | selection of Body |
-| main.go:17:10:17:15 | selection of Form |
-| main.go:18:10:18:17 | selection of Header |
-| main.go:19:10:19:14 | selection of URL |
-| main.go:23:10:23:16 | selection of Body |
-| main.go:24:10:24:16 | selection of Form |
-| main.go:25:10:25:18 | selection of Header |
-| main.go:26:10:26:15 | selection of URL |
-| main.go:48:2:48:11 | selection of Header |
+| main.go:17:10:17:15 | selection of Body |
+| main.go:18:10:18:15 | selection of Form |
+| main.go:19:10:19:17 | selection of Header |
+| main.go:20:10:20:14 | selection of URL |
+| main.go:24:10:24:16 | selection of Body |
+| main.go:25:10:25:16 | selection of Form |
+| main.go:26:10:26:18 | selection of Header |
+| main.go:27:10:27:15 | selection of URL |
 | main.go:49:2:49:11 | selection of Header |
 | main.go:50:2:50:11 | selection of Header |
+| main.go:51:2:51:11 | selection of Header |
+| main.go:63:49:63:53 | selection of URL |
 | server.go:8:6:8:13 | selection of Header |
 | server.go:9:6:9:13 | selection of Header |
 | server.go:10:6:10:13 | selection of Header |
diff --git a/ql/test/library-tests/semmle/go/concepts/HTTP/main.go b/ql/test/library-tests/semmle/go/concepts/HTTP/main.go
index cb8e8a85b43..7abf0a170c0 100644
--- a/ql/test/library-tests/semmle/go/concepts/HTTP/main.go
+++ b/ql/test/library-tests/semmle/go/concepts/HTTP/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"fmt"
+	"html"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -55,4 +56,10 @@ func main() {
 
 	resp, _ := http.Get("https://example.com")
 	resp.Header.Set("This-Makes", "No sense")
+
+	http.HandleFunc("/foo", handler) // $handler="/foo"
+
+	http.HandleFunc("/bar", func(w http.ResponseWriter, r *http.Request) { // $handler="/bar"
+		fmt.Fprintf(w, "Hello, %q", html.EscapeString(r.URL.Path))
+	})
 }
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/go.mod b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/go.mod
new file mode 100644
index 00000000000..21f5e109021
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/go.mod
@@ -0,0 +1,8 @@
+module main
+
+go 1.14
+
+require (
+	github.com/elazarl/goproxy v0.0.0-20201021153353-00ad82a08272
+	github.com/github/depstubber v0.0.0-20201214172518-12c3da4b7c9d // indirect
+)
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/main.go b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/main.go
new file mode 100644
index 00000000000..5c5f104e1b2
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/main.go
@@ -0,0 +1,27 @@
+//go:generate depstubber -vendor github.com/elazarl/goproxy ProxyCtx NewResponse,TextResponse,AlwaysReject,ContentTypeText,ContentTypeHtml,ReqHostMatches
+
+package main
+
+import (
+	"fmt"
+	"github.com/elazarl/goproxy"
+	"net/http"
+)
+
+func handler(r *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
+	data := ctx.UserData // $untrustedflowsource=selection of UserData
+
+	// note no content type result here because we don't seem to extract the value of `ContentTypeHtml`
+	return r, goproxy.NewResponse(r, goproxy.ContentTypeHtml, http.StatusForbidden, fmt.Sprintf("<body>Bad request: %v</body>", data)) // $headerwrite=status:403
+}
+
+func handler1(r *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
+	ctx.Logf("test")   // $logger="test"
+	ctx.Warnf("test1") // $logger="test1"
+
+	return r, goproxy.TextResponse(r, "Hello!") // $headerwrite=status:200 $headerwrite=content-type:text/plain
+}
+
+func main() {
+
+}
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/test.expected b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/test.expected
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/test.ql b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/test.ql
new file mode 100644
index 00000000000..cf7ff09fb3f
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/test.ql
@@ -0,0 +1,46 @@
+import go
+import TestUtilities.InlineExpectationsTest
+
+class UntrustedFlowSourceTest extends InlineExpectationsTest {
+  UntrustedFlowSourceTest() { this = "untrustedflowsource" }
+
+  override string getARelevantTag() { result = "untrustedflowsource" }
+
+  override predicate hasActualResult(string file, int line, string element, string tag, string value) {
+    tag = "untrustedflowsource" and
+    value = element and
+    exists(UntrustedFlowSource src | value = src.toString() |
+      src.hasLocationInfo(file, line, _, _, _)
+    )
+  }
+}
+
+class HeaderWriteTest extends InlineExpectationsTest {
+  HeaderWriteTest() { this = "headerwrite" }
+
+  override string getARelevantTag() { result = "headerwrite" }
+
+  override predicate hasActualResult(string file, int line, string element, string tag, string value) {
+    tag = "headerwrite" and
+    exists(HTTP::HeaderWrite hw, string name, string val | element = hw.toString() |
+      hw.definesHeader(name, val) and
+      value = name + ":" + val and
+      hw.hasLocationInfo(file, line, _, _, _)
+    )
+  }
+}
+
+class LoggerTest extends InlineExpectationsTest {
+  LoggerTest() { this = "LoggerTest" }
+
+  override string getARelevantTag() { result = "logger" }
+
+  override predicate hasActualResult(string file, int line, string element, string tag, string value) {
+    exists(LoggerCall log |
+      log.hasLocationInfo(file, line, _, _, _) and
+      element = log.toString() and
+      value = log.getAMessageComponent().toString() and
+      tag = "logger"
+    )
+  }
+}
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/.gitignore b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/.gitignore
new file mode 100644
index 00000000000..1005f6f1ecd
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/.gitignore
@@ -0,0 +1,2 @@
+bin
+*.swp
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/LICENSE b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/LICENSE
new file mode 100644
index 00000000000..2067e567c9f
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2012 Elazar Leibovich. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Elazar Leibovich. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/stub.go b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/stub.go
new file mode 100644
index 00000000000..3d4882efc8b
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/github.com/elazarl/goproxy/stub.go
@@ -0,0 +1,159 @@
+// Code generated by depstubber. DO NOT EDIT.
+// This is a simple stub for github.com/elazarl/goproxy, strictly for use in testing.
+
+// See the LICENSE file for information about the licensing of the original library.
+// Source: github.com/elazarl/goproxy (exports: ProxyCtx; functions: NewResponse,TextResponse,AlwaysReject,ContentTypeText,ContentTypeHtml,ReqHostMatches)
+
+// Package goproxy is a stub of github.com/elazarl/goproxy, generated by depstubber.
+package goproxy
+
+import (
+	tls "crypto/tls"
+	net "net"
+	http "net/http"
+	regexp "regexp"
+)
+
+var AlwaysReject FuncHttpsHandler = nil
+
+type CertStorage interface {
+	Fetch(_ string, _ func() (*tls.Certificate, error)) (*tls.Certificate, error)
+}
+
+type ConnectAction struct {
+	Action    ConnectActionLiteral
+	Hijack    func(*http.Request, net.Conn, *ProxyCtx)
+	TLSConfig func(string, *ProxyCtx) (*tls.Config, error)
+}
+
+type ConnectActionLiteral int
+
+var ContentTypeHtml string = ""
+
+var ContentTypeText string = ""
+
+type FuncHttpsHandler func(string, *ProxyCtx) (*ConnectAction, string)
+
+func (_ FuncHttpsHandler) HandleConnect(_ string, _ *ProxyCtx) (*ConnectAction, string) {
+	return nil, ""
+}
+
+type HttpsHandler interface {
+	HandleConnect(_ string, _ *ProxyCtx) (*ConnectAction, string)
+}
+
+type Logger interface {
+	Printf(_ string, _ ...interface{})
+}
+
+func NewResponse(_ *http.Request, _ string, _ int, _ string) *http.Response {
+	return nil
+}
+
+type ProxyConds struct{}
+
+func (_ *ProxyConds) Do(_ RespHandler) {}
+
+func (_ *ProxyConds) DoFunc(_ func(*http.Response, *ProxyCtx) *http.Response) {}
+
+type ProxyCtx struct {
+	Req          *http.Request
+	Resp         *http.Response
+	RoundTripper RoundTripper
+	Error        error
+	UserData     interface{}
+	Session      int64
+	Proxy        *ProxyHttpServer
+}
+
+func (_ *ProxyCtx) Charset() string {
+	return ""
+}
+
+func (_ *ProxyCtx) Logf(_ string, _ ...interface{}) {}
+
+func (_ *ProxyCtx) RoundTrip(_ *http.Request) (*http.Response, error) {
+	return nil, nil
+}
+
+func (_ *ProxyCtx) Warnf(_ string, _ ...interface{}) {}
+
+type ProxyHttpServer struct {
+	KeepDestinationHeaders bool
+	Verbose                bool
+	Logger                 Logger
+	NonproxyHandler        http.Handler
+	Tr                     *http.Transport
+	ConnectDial            func(string, string) (net.Conn, error)
+	CertStore              CertStorage
+	KeepHeader             bool
+}
+
+func (_ *ProxyHttpServer) NewConnectDialToProxy(_ string) func(string, string) (net.Conn, error) {
+	return nil
+}
+
+func (_ *ProxyHttpServer) NewConnectDialToProxyWithHandler(_ string, _ func(*http.Request)) func(string, string) (net.Conn, error) {
+	return nil
+}
+
+func (_ *ProxyHttpServer) OnRequest(_ ...ReqCondition) *ReqProxyConds {
+	return nil
+}
+
+func (_ *ProxyHttpServer) OnResponse(_ ...RespCondition) *ProxyConds {
+	return nil
+}
+
+func (_ *ProxyHttpServer) ServeHTTP(_ http.ResponseWriter, _ *http.Request) {}
+
+type ReqCondition interface {
+	HandleReq(_ *http.Request, _ *ProxyCtx) bool
+	HandleResp(_ *http.Response, _ *ProxyCtx) bool
+}
+
+type ReqConditionFunc func(*http.Request, *ProxyCtx) bool
+
+func (_ ReqConditionFunc) HandleReq(_ *http.Request, _ *ProxyCtx) bool {
+	return false
+}
+
+func (_ ReqConditionFunc) HandleResp(_ *http.Response, _ *ProxyCtx) bool {
+	return false
+}
+
+type ReqHandler interface {
+	Handle(_ *http.Request, _ *ProxyCtx) (*http.Request, *http.Response)
+}
+
+func ReqHostMatches(_ ...*regexp.Regexp) ReqConditionFunc {
+	return nil
+}
+
+type ReqProxyConds struct{}
+
+func (_ *ReqProxyConds) Do(_ ReqHandler) {}
+
+func (_ *ReqProxyConds) DoFunc(_ func(*http.Request, *ProxyCtx) (*http.Request, *http.Response)) {}
+
+func (_ *ReqProxyConds) HandleConnect(_ HttpsHandler) {}
+
+func (_ *ReqProxyConds) HandleConnectFunc(_ func(string, *ProxyCtx) (*ConnectAction, string)) {}
+
+func (_ *ReqProxyConds) HijackConnect(_ func(*http.Request, net.Conn, *ProxyCtx)) {}
+
+type RespCondition interface {
+	HandleResp(_ *http.Response, _ *ProxyCtx) bool
+}
+
+type RespHandler interface {
+	Handle(_ *http.Response, _ *ProxyCtx) *http.Response
+}
+
+type RoundTripper interface {
+	RoundTrip(_ *http.Request, _ *ProxyCtx) (*http.Response, error)
+}
+
+func TextResponse(_ *http.Request, _ string) *http.Response {
+	return nil
+}
diff --git a/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/modules.txt b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/modules.txt
new file mode 100644
index 00000000000..bf027718a74
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/frameworks/ElazarlGoproxy/vendor/modules.txt
@@ -0,0 +1,5 @@
+# github.com/elazarl/goproxy v0.0.0-20201021153353-00ad82a08272
+## explicit
+github.com/elazarl/goproxy
+# github.com/github/depstubber v0.0.0-20201214172518-12c3da4b7c9d
+## explicit
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/IncompleteHostnameRegexp.expected b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/IncompleteHostnameRegexp.expected
index 73231e52340..bff95f0497d 100644
--- a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/IncompleteHostnameRegexp.expected
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/IncompleteHostnameRegexp.expected
@@ -3,7 +3,9 @@ edges
 nodes
 | IncompleteHostnameRegexp.go:11:8:11:36 | "^((www\|beta).)?example.com/" : string | semmle.label | "^((www\|beta).)?example.com/" : string |
 | IncompleteHostnameRegexp.go:12:38:12:39 | re | semmle.label | re |
-| main.go:12:15:12:39 | `https://www.example.com` | semmle.label | `https://www.example.com` |
+| main.go:39:60:39:79 | "^test2.github.com$" | semmle.label | "^test2.github.com$" |
+| main.go:44:15:44:39 | `https://www.example.com` | semmle.label | `https://www.example.com` |
 #select
 | IncompleteHostnameRegexp.go:11:8:11:36 | "^((www\|beta).)?example.com/" : string | IncompleteHostnameRegexp.go:11:8:11:36 | "^((www\|beta).)?example.com/" : string | IncompleteHostnameRegexp.go:12:38:12:39 | re | This regular expression has an unescaped dot before ')?example.com', so it might match more hosts than expected when used $@. | IncompleteHostnameRegexp.go:12:38:12:39 | re | here |
-| main.go:12:15:12:39 | `https://www.example.com` | main.go:12:15:12:39 | `https://www.example.com` | main.go:12:15:12:39 | `https://www.example.com` | This regular expression has an unescaped dot before 'example.com', so it might match more hosts than expected when used $@. | main.go:12:15:12:39 | `https://www.example.com` | here |
+| main.go:39:60:39:79 | "^test2.github.com$" | main.go:39:60:39:79 | "^test2.github.com$" | main.go:39:60:39:79 | "^test2.github.com$" | This regular expression has an unescaped dot before 'github.com', so it might match more hosts than expected when used $@. | main.go:39:60:39:79 | "^test2.github.com$" | here |
+| main.go:44:15:44:39 | `https://www.example.com` | main.go:44:15:44:39 | `https://www.example.com` | main.go:44:15:44:39 | `https://www.example.com` | This regular expression has an unescaped dot before 'example.com', so it might match more hosts than expected when used $@. | main.go:44:15:44:39 | `https://www.example.com` | here |
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/go.mod b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/go.mod
new file mode 100644
index 00000000000..a77ab8418f8
--- /dev/null
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/go.mod
@@ -0,0 +1,7 @@
+module main
+
+go 1.14
+
+require (
+	github.com/elazarl/goproxy v0.0.0-20201021153353-00ad82a08272
+)
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/main.go b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/main.go
index 81123454971..fb1e5b77b51 100644
--- a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/main.go
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/main.go
@@ -1,13 +1,45 @@
+//go:generate depstubber -vendor github.com/elazarl/goproxy ProxyCtx NewProxyHttpServer,NewResponse,AlwaysReject,ContentTypeText,ReqHostMatches
+
 package main
 
 import (
+	"github.com/elazarl/goproxy"
+	"net/http"
 	"regexp"
+	"time"
 )
 
 func Match(notARegex string) bool {
 	return notARegex != ""
 }
 
+func stdlibreject(w http.ResponseWriter, r *http.Request) {
+	if matched, _ := regexp.MatchString(`test.github.com`, r.URL.String()); matched {
+		http.Error(w, "Bad request!", http.StatusBadRequest)
+	}
+}
+
+func sometimesReject(req *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
+	if h, _, _ := time.Now().Clock(); h >= 8 && h <= 17 {
+		return req, goproxy.NewResponse(req, goproxy.ContentTypeText, http.StatusForbidden, "Bad request!")
+	}
+	return req, nil
+}
+
+func reject(req *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
+	return req, goproxy.NewResponse(req, goproxy.ContentTypeText, http.StatusForbidden, "Bad request!")
+}
+
+func proxy() {
+	proxy := goproxy.NewProxyHttpServer()
+	proxy.OnRequest(goproxy.ReqHostMatches(regexp.MustCompile("^test.github.com$"))).
+		HandleConnect(goproxy.AlwaysReject) // OK (rejecting all requests)
+	proxy.OnRequest(goproxy.ReqHostMatches(regexp.MustCompile("^test1.github.com$"))).
+		DoFunc(reject) // OK (rejecting all requests)
+	proxy.OnRequest(goproxy.ReqHostMatches(regexp.MustCompile("^test2.github.com$"))).
+		DoFunc(sometimesReject) // NOT OK (sometimes accepts requests)
+}
+
 func main() {
 	regexp.Match(`https://www.example.com`, []byte(""))   // NOT OK
 	regexp.Match(`https://www\.example\.com`, []byte("")) // OK
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/.gitignore b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/.gitignore
new file mode 100644
index 00000000000..1005f6f1ecd
--- /dev/null
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/.gitignore
@@ -0,0 +1,2 @@
+bin
+*.swp
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/LICENSE b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/LICENSE
new file mode 100644
index 00000000000..2067e567c9f
--- /dev/null
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2012 Elazar Leibovich. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Elazar Leibovich. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/stub.go b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/stub.go
new file mode 100644
index 00000000000..62277c6e4ac
--- /dev/null
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/github.com/elazarl/goproxy/stub.go
@@ -0,0 +1,157 @@
+// Code generated by depstubber. DO NOT EDIT.
+// This is a simple stub for github.com/elazarl/goproxy, strictly for use in testing.
+
+// See the LICENSE file for information about the licensing of the original library.
+// Source: github.com/elazarl/goproxy (exports: ProxyCtx; functions: NewProxyHttpServer,NewResponse,AlwaysReject,ContentTypeText,ReqHostMatches)
+
+// Package goproxy is a stub of github.com/elazarl/goproxy, generated by depstubber.
+package goproxy
+
+import (
+	tls "crypto/tls"
+	net "net"
+	http "net/http"
+	regexp "regexp"
+)
+
+var AlwaysReject FuncHttpsHandler = nil
+
+type CertStorage interface {
+	Fetch(_ string, _ func() (*tls.Certificate, error)) (*tls.Certificate, error)
+}
+
+type ConnectAction struct {
+	Action    ConnectActionLiteral
+	Hijack    func(*http.Request, net.Conn, *ProxyCtx)
+	TLSConfig func(string, *ProxyCtx) (*tls.Config, error)
+}
+
+type ConnectActionLiteral int
+
+var ContentTypeText string = ""
+
+type FuncHttpsHandler func(string, *ProxyCtx) (*ConnectAction, string)
+
+func (_ FuncHttpsHandler) HandleConnect(_ string, _ *ProxyCtx) (*ConnectAction, string) {
+	return nil, ""
+}
+
+type HttpsHandler interface {
+	HandleConnect(_ string, _ *ProxyCtx) (*ConnectAction, string)
+}
+
+type Logger interface {
+	Printf(_ string, _ ...interface{})
+}
+
+func NewProxyHttpServer() *ProxyHttpServer {
+	return nil
+}
+
+func NewResponse(_ *http.Request, _ string, _ int, _ string) *http.Response {
+	return nil
+}
+
+type ProxyConds struct{}
+
+func (_ *ProxyConds) Do(_ RespHandler) {}
+
+func (_ *ProxyConds) DoFunc(_ func(*http.Response, *ProxyCtx) *http.Response) {}
+
+type ProxyCtx struct {
+	Req          *http.Request
+	Resp         *http.Response
+	RoundTripper RoundTripper
+	Error        error
+	UserData     interface{}
+	Session      int64
+	Proxy        *ProxyHttpServer
+}
+
+func (_ *ProxyCtx) Charset() string {
+	return ""
+}
+
+func (_ *ProxyCtx) Logf(_ string, _ ...interface{}) {}
+
+func (_ *ProxyCtx) RoundTrip(_ *http.Request) (*http.Response, error) {
+	return nil, nil
+}
+
+func (_ *ProxyCtx) Warnf(_ string, _ ...interface{}) {}
+
+type ProxyHttpServer struct {
+	KeepDestinationHeaders bool
+	Verbose                bool
+	Logger                 Logger
+	NonproxyHandler        http.Handler
+	Tr                     *http.Transport
+	ConnectDial            func(string, string) (net.Conn, error)
+	CertStore              CertStorage
+	KeepHeader             bool
+}
+
+func (_ *ProxyHttpServer) NewConnectDialToProxy(_ string) func(string, string) (net.Conn, error) {
+	return nil
+}
+
+func (_ *ProxyHttpServer) NewConnectDialToProxyWithHandler(_ string, _ func(*http.Request)) func(string, string) (net.Conn, error) {
+	return nil
+}
+
+func (_ *ProxyHttpServer) OnRequest(_ ...ReqCondition) *ReqProxyConds {
+	return nil
+}
+
+func (_ *ProxyHttpServer) OnResponse(_ ...RespCondition) *ProxyConds {
+	return nil
+}
+
+func (_ *ProxyHttpServer) ServeHTTP(_ http.ResponseWriter, _ *http.Request) {}
+
+type ReqCondition interface {
+	HandleReq(_ *http.Request, _ *ProxyCtx) bool
+	HandleResp(_ *http.Response, _ *ProxyCtx) bool
+}
+
+type ReqConditionFunc func(*http.Request, *ProxyCtx) bool
+
+func (_ ReqConditionFunc) HandleReq(_ *http.Request, _ *ProxyCtx) bool {
+	return false
+}
+
+func (_ ReqConditionFunc) HandleResp(_ *http.Response, _ *ProxyCtx) bool {
+	return false
+}
+
+type ReqHandler interface {
+	Handle(_ *http.Request, _ *ProxyCtx) (*http.Request, *http.Response)
+}
+
+func ReqHostMatches(_ ...*regexp.Regexp) ReqConditionFunc {
+	return nil
+}
+
+type ReqProxyConds struct{}
+
+func (_ *ReqProxyConds) Do(_ ReqHandler) {}
+
+func (_ *ReqProxyConds) DoFunc(_ func(*http.Request, *ProxyCtx) (*http.Request, *http.Response)) {}
+
+func (_ *ReqProxyConds) HandleConnect(_ HttpsHandler) {}
+
+func (_ *ReqProxyConds) HandleConnectFunc(_ func(string, *ProxyCtx) (*ConnectAction, string)) {}
+
+func (_ *ReqProxyConds) HijackConnect(_ func(*http.Request, net.Conn, *ProxyCtx)) {}
+
+type RespCondition interface {
+	HandleResp(_ *http.Response, _ *ProxyCtx) bool
+}
+
+type RespHandler interface {
+	Handle(_ *http.Response, _ *ProxyCtx) *http.Response
+}
+
+type RoundTripper interface {
+	RoundTrip(_ *http.Request, _ *ProxyCtx) (*http.Response, error)
+}
diff --git a/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/modules.txt b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/modules.txt
new file mode 100644
index 00000000000..bf027718a74
--- /dev/null
+++ b/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegexp/vendor/modules.txt
@@ -0,0 +1,5 @@
+# github.com/elazarl/goproxy v0.0.0-20201021153353-00ad82a08272
+## explicit
+github.com/elazarl/goproxy
+# github.com/github/depstubber v0.0.0-20201214172518-12c3da4b7c9d
+## explicit