Add nimtwirp.validateRequest()

Move request validation to a separate proc instead of generating the checks
inline for all handleRequest() procs.

2 files changed, 18 insertions, 10 deletions

diff --git a/nimtwirp/generator.nim b/nimtwirp/generator.nim
index 167ad17..e3f94b2 100644
--- a/nimtwirp/generator.nim
+++ b/nimtwirp/generator.nim
@@ -54,16 +54,7 @@ proc new{service.name}*(): {service.name} =
     new(result)
 
 proc handleRequest*(service: {service.name}, req: Request): Future[nimtwirp.Response] {{.async.}} =
-    if req.reqMethod != HttpPost:
-        raise newTwirpError(TwirpBadRoute, "only POST accepted")
-
-    if getOrDefault(req.headers, "Content-Type") != "application/protobuf":
-        raise newTwirpError(TwirpInternal, "invalid Content-Type")
-
-    if not startsWith(req.url.path, {service.name}Prefix):
-        raise newTwirpError(TwirpBadRoute, "unknown service")
-
-    let methodName = req.url.path[len({service.name}Prefix)..^1]
+    let (_, methodName) = validateRequest(req, {service.name}Prefix)
 
 """
 
diff --git a/nimtwirp/nimtwirp.nim b/nimtwirp/nimtwirp.nim
index 7c30980..f3fa29d 100644
--- a/nimtwirp/nimtwirp.nim
+++ b/nimtwirp/nimtwirp.nim
@@ -4,6 +4,7 @@ import httpclient
 import json
 import macros
 import strformat
+import strutils
 
 import errors
 
@@ -116,3 +117,19 @@ proc request*(client: Client, prefix: string, meth: string, body: string): httpc
             raise newTwirpError(TwirpInternal, "Invalid Content-Type in response")
         let errorInfo = parseJson(result.body)
         raise twirpErrorFromJson(errorInfo)
+
+proc validateRequest*(request: asynchttpserver.Request, prefix: string): tuple[contentType: string, methodName: string] =
+    if request.reqMethod != HttpPost:
+        raise newTwirpError(TwirpBadRoute, "only POST accepted")
+
+    result.contentType = getOrDefault(request.headers, "Content-Type")
+
+    if result.contentType != "application/protobuf":
+        raise newTwirpError(TwirpInternal,
+            "expected Content-Type to be application/protobuf instead of " &
+            result.contentType)
+
+    if not startsWith(request.url.path, prefix):
+        raise newTwirpError(TwirpBadRoute, "unknown service")
+
+    result.methodName = request.url.path[len(prefix)..^1]