Use clearer replacement syntax

Author: Integralist

Makefile

@@ -1,5 +1,5 @@
 test:
-	go test -v ./...
+	go test -v -failfast ./...
 
 run:
 	go run main.go

README.md

@@ -70,7 +70,7 @@ Both requests will be proxied straight through to the specified upstream without
 Config{
   Path:       `/(?P<cap>foo\w{3})`,
   Upstream:   upstreams.HTTPBin,
-  ModifyPath: "/anything/$cap",
+  ModifyPath: "/anything/${cap}",
 }
 ```
 
@@ -94,7 +94,7 @@ Config{
   Override: Override{
     Header:     "X-BF-Testing",
     Match:      "integralist",
-    ModifyPath: "/anything/newthing$cap",
+    ModifyPath: "/anything/newthing${cap}",
   },
 }
 ```
@@ -118,11 +118,11 @@ If the relevant request header is specified, then the request will be proxied th
 Config{
   Path:       "/(?P<cap>double-checks)$",
   Upstream:   upstreams.HTTPBin,
-  ModifyPath: "/anything/toplevel-modified-$cap",
+  ModifyPath: "/anything/toplevel-modified-${cap}",
   Override: Override{
     Header:     "X-BF-Testing",
     Match:      "integralist",
-    ModifyPath: "/anything/override-modified-$cap",
+    ModifyPath: "/anything/override-modified-${cap}",
   },
 }
 ```
@@ -207,7 +207,7 @@ Config{
     Query:      "s",
     Match:      `integralist(?P<cap>\d{1,3})$`,
     MatchType:  "regex",
-    ModifyPath: "/anything/newthing$cap",
+    ModifyPath: "/anything/newthing${cap}",
   },
 }
 ```

proxy/proxy.go

@@ -97,7 +97,8 @@ func modifyPath(req *http.Request, modifyPath string) {
 			if isCaptureGroup {
 				// interpolate query param value into modified request path
 				cleanKeyPrefix := strings.Replace(k, "ncg_", "", 1)
-				r := strings.NewReplacer("$", "", cleanKeyPrefix, v[0])
+				// replace ${foo} with foo
+				r := strings.NewReplacer("$", "", "{", "", "}", "", cleanKeyPrefix, v[0])
 				req.URL.Path = r.Replace(req.URL.Path)
 			}
 		}
@@ -122,7 +123,8 @@ func overrideHeader(req *http.Request, override routing.Override) {
 					if isCaptureGroup {
 						// interpolate query param value into modified request path
 						cleanKeyPrefix := strings.Replace(k, "ncg_", "", 1)
-						r := strings.NewReplacer("$", "", cleanKeyPrefix, v[0])
+						// replace ${foo} with foo
+						r := strings.NewReplacer("$", "", "{", "", "}", "", cleanKeyPrefix, v[0])
 						req.URL.Path = r.Replace(req.URL.Path)
 					}
 				}

routing/configuration.go

@@ -37,17 +37,17 @@ var Configuration = []Config{
 		Override: Override{
 			Header:     "X-BF-Testing",
 			Match:      "integralist",
-			ModifyPath: "/anything/newthing$cap",
+			ModifyPath: "/anything/newthing${cap}",
 		},
 	},
 	Config{
 		Path:       "/(?P<cap>double-checks)$",
 		Upstream:   upstreams.HTTPBin,
-		ModifyPath: "/anything/toplevel-modified-$cap",
+		ModifyPath: "/anything/toplevel-modified-${cap}",
 		Override: Override{
 			Header:     "X-BF-Testing",
 			Match:      "integralist",
-			ModifyPath: "/anything/override-modified-$cap",
+			ModifyPath: "/anything/override-modified-${cap}",
 		},
 	},
 	Config{
@@ -76,13 +76,13 @@ var Configuration = []Config{
 			Query:      "s",
 			Match:      `integralist(?P<cap>\d{1,3})$`,
 			MatchType:  "regex",
-			ModifyPath: "/anything/newthing$cap",
+			ModifyPath: "/anything/newthing${cap}",
 		},
 	},
 	Config{
 		Path:       `/(?P<cap>foo\w{3})`,
 		Upstream:   upstreams.HTTPBin,
-		ModifyPath: "/anything/$cap",
+		ModifyPath: "/anything/${cap}",
 	},
 	Config{
 		Path:       "/beep(?P<cap>boop)",