Add utility to format HTTP requests as curl

Author: tulir

exfmt/curl.go

@@ -0,0 +1,68 @@
+// Copyright (c) 2024 Tulir Asokan
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package exfmt
+
+import (
+	"encoding/base64"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+)
+
+// FormatCurl formats the given HTTP request as a curl command.
+//
+// This will include all headers, and also the request body if GetBody is set. Notes:
+//
+// * Header names are quoted using fmt.Sprintf, so it may not always be correct for shell quoting.
+// * The URL is only quoted and not escaped, so URLs with single quotes will not currently work.
+//
+// The client parameter is optional and is used to find cookies from the cookie jar.
+func FormatCurl(cli *http.Client, req *http.Request) string {
+	var curl []string
+	hasBody := false
+	if req.GetBody != nil {
+		body, _ := req.GetBody()
+		if body != http.NoBody {
+			b, _ := io.ReadAll(body)
+			curl = []string{"echo", base64.StdEncoding.EncodeToString(b), "|", "base64", "-d", "|"}
+			hasBody = true
+		}
+	}
+	curl = append(curl, "curl", "-v")
+	switch req.Method {
+	case http.MethodGet:
+		// Don't add -X
+	case http.MethodHead:
+		curl = append(curl, "-I")
+	default:
+		curl = append(curl, "-X", req.Method)
+	}
+	for key, vals := range req.Header {
+		kv := fmt.Sprintf("%s: %s", key, vals[0])
+		curl = append(curl, "-H", fmt.Sprintf("%q", kv))
+	}
+	if cli != nil && cli.Jar != nil {
+		cookies := cli.Jar.Cookies(req.URL)
+		if len(cookies) > 0 {
+			cookieStrings := make([]string, len(cookies))
+			for i, cookie := range cookies {
+				if strings.ContainsAny(cookie.Value, " ,") {
+					cookieStrings[i] = fmt.Sprintf(`%s="%s"`, cookie.Name, cookie.Value)
+				} else {
+					cookieStrings[i] = fmt.Sprintf("%s=%s", cookie.Name, cookie.Value)
+				}
+			}
+			curl = append(curl, "-H", fmt.Sprintf("%q", "Cookie: "+strings.Join(cookieStrings, "; ")))
+		}
+	}
+	if hasBody {
+		curl = append(curl, "--data-binary", "@-")
+	}
+	curl = append(curl, fmt.Sprintf("'%s'", req.URL.String()))
+	return strings.Join(curl, " ")
+}