From 1e5c86eeb045499f248a8393b8a28409d561b286 Mon Sep 17 00:00:00 2001
From: Graham Crowell <grahamcrowell@users.noreply.github.com>
Date: Thu, 12 Jan 2023 06:50:17 -0800
Subject: [PATCH] #741 uri cache mutex (#742)

---
 .github/workflows/go.yml      |  3 +++
 openapi3/issue741_test.go     | 43 +++++++++++++++++++++++++++++++++++
 openapi3/loader_uri_reader.go |  8 +++++++
 3 files changed, 54 insertions(+)
 create mode 100644 openapi3/issue741_test.go

diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index b38f10fba..8dbb0620f 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -79,6 +79,9 @@ jobs:
     - run: go test -v -run TestRaceyPatternSchema -race ./...
       env:
         CGO_ENABLED: '1'
+    - run: go test -v -run TestIssue741 -race ./...
+      env:
+        CGO_ENABLED: '1'
     - run: git --no-pager diff --exit-code
 
     - if: runner.os == 'Linux'
diff --git a/openapi3/issue741_test.go b/openapi3/issue741_test.go
new file mode 100644
index 000000000..aad522023
--- /dev/null
+++ b/openapi3/issue741_test.go
@@ -0,0 +1,43 @@
+package openapi3
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIssue741(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		body := `{"openapi":"3.0.0","info":{"title":"MyAPI","version":"0.1","description":"An API"},"paths":{},"components":{"schemas":{"Foo":{"type":"string"}}}}`
+		_, err := w.Write([]byte(body))
+		if err != nil {
+			panic(err)
+		}
+	}))
+	defer ts.Close()
+
+	rootSpec := []byte(fmt.Sprintf(
+		`{"openapi":"3.0.0","info":{"title":"MyAPI","version":"0.1","description":"An API"},"paths":{},"components":{"schemas":{"Bar1":{"$ref":"%s#/components/schemas/Foo"}}}}`,
+		ts.URL,
+	))
+
+	wg := &sync.WaitGroup{}
+	n := 10
+	for i := 0; i < n; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			loader := NewLoader()
+			loader.IsExternalRefsAllowed = true
+			doc, err := loader.LoadFromData(rootSpec)
+			require.NoError(t, err)
+			require.NotNil(t, doc)
+		}()
+	}
+	wg.Wait()
+}
diff --git a/openapi3/loader_uri_reader.go b/openapi3/loader_uri_reader.go
index 8357a980d..92ac043f9 100644
--- a/openapi3/loader_uri_reader.go
+++ b/openapi3/loader_uri_reader.go
@@ -7,12 +7,15 @@ import (
 	"net/http"
 	"net/url"
 	"path/filepath"
+	"sync"
 )
 
 // ReadFromURIFunc defines a function which reads the contents of a resource
 // located at a URI.
 type ReadFromURIFunc func(loader *Loader, url *url.URL) ([]byte, error)
 
+var uriMu = &sync.RWMutex{}
+
 // ErrURINotSupported indicates the ReadFromURIFunc does not know how to handle a
 // given URI.
 var ErrURINotSupported = errors.New("unsupported URI")
@@ -92,12 +95,17 @@ func URIMapCache(reader ReadFromURIFunc) ReadFromURIFunc {
 		}
 		uri := location.String()
 		var ok bool
+		uriMu.RLock()
 		if buf, ok = cache[uri]; ok {
+			uriMu.RUnlock()
 			return
 		}
+		uriMu.RUnlock()
 		if buf, err = reader(loader, location); err != nil {
 			return
 		}
+		uriMu.Lock()
+		defer uriMu.Unlock()
 		cache[uri] = buf
 		return
 	}