Add utilities for handling the traceparent header (see Trace Context W3C standard).

- Allow the caller to optionally provide a list
- Add `traceparent`, `tracestate`, `X-Request-ID` and `X-Correlation-Id`
  by default.

buffoonery.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "0.4.7"
+version       = "0.4.9"
 author        = "Jonathan Bernard"
 description   = "Jonathan's opinionated extensions and auth layer for Jester."
 license       = "MIT"

src/buffoonery/apiutils.nim

@@ -1,5 +1,5 @@
 import std/[json, jsonutils, options, sequtils, strtabs, strutils]
-import mummy, webby
+import mummy, webby, uuids
 
 import std/httpcore except HttpHeaders
 
@@ -47,6 +47,7 @@ func `$`*(r: ApiResponse): string = $(%r)
 proc makeCorsHeaders*(
     allowedMethods: seq[string],
     allowedOrigins: seq[string],
+    allowedHeaders: Option[seq[string]],
     reqOrigin = none[string]()): HttpHeaders =
 
   result =
@@ -54,8 +55,13 @@ proc makeCorsHeaders*(
       @{
         "Access-Control-Allow-Origin": reqOrigin.get,
         "Access-Control-Allow-Credentials": "true",
-        "Access-Control-Allow-Methods": allowedMethods.join(", "),
-        "Access-Control-Allow-Headers": "DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization,X-CSRF-TOKEN"
+        "Access-Control-Allow-Methods": allowedMethods.join(","),
+        "Access-Control-Allow-Headers":
+          if allowedHeaders.isSome: allowedHeaders.get.join(",")
+          else:
+            "DNT,User-Agent,X-Requested-With,If-Modified-Since," &
+            "Cache-Control,Content-Type,Range,Authorization,X-CSRF-TOKEN," &
+            "traceparent,tracestate,X-Request-ID,X-Correlation-ID",
       }
     else:
       if reqOrigin.isSome:
@@ -67,8 +73,16 @@ proc makeCorsHeaders*(
 proc makeCorsHeaders*(
     allowedMethods: seq[HttpMethod],
     allowedOrigins: seq[string],
+    allowedHeaders: Option[seq[string]],
     reqOrigin = none[string]()): HttpHeaders =
- makeCorsHeaders(allowedMethods.mapIt($it), allowedOrigins, reqOrigin )
+ makeCorsHeaders(allowedMethods.mapIt($it), allowedOrigins, allowedHeaders, reqOrigin )
+
+
+proc makeCorsHeaders*[T: HttpMethod or string](
+    allowedMethods: seq[T],
+    allowedOrigins: seq[string],
+    reqOrigin = none[string]()): HttpHeaders =
+ makeCorsHeaders(allowedMethods, allowedOrigins, none[seq[string]](), reqOrigin )
 
 
 func origin*(req: Request): Option[string] =
@@ -76,6 +90,40 @@ func origin*(req: Request): Option[string] =
   else: none[string]()
 
 
+func traceparent*(req: Request): Option[string] =
+  ## Extract the traceparent from the request headers, if present.
+  if req.headers.contains("traceparent"):
+    return some(req.headers["traceparent"])
+  else:
+    return none[string]()
+
+
+proc makeTraceContextHeaders*(req: Request, traceParentId: string): HttpHeaders =
+  var headers = HttpHeaders(@[])
+
+  if req.headers.contains("traceparent"):
+    # If the traceparent header is present, we should update it with our
+    # parent-id.
+    let traceparentParts = req.headers["traceparent"].split("-")
+    if traceparentParts.len != 4:
+      headers["traceparent"] = "00-$#-$#-00" % [
+        replace($genUUID(), "-", ""), # trace-id
+        traceParentId,                # parent-id
+      ]
+
+    else:
+      headers["traceparent"] = "00-$#-$#-$#" % [
+        traceparentParts[1], # trace-id
+        traceParentId,       # parent-id
+        traceparentParts[3], # flags
+      ]
+
+    if req.headers.contains("tracestate"):
+      headers["tracestate"] = req.headers["tracestate"]
+
+  return headers
+
+
 proc respondWithRawJson*(
     req: Request,
     body: JsonNode,