return server exception message on api exception

This change is to return the exception encountered while executing server function back to the client.
The exception is returned in string form in the `data` field of the error response.

To customize messages at server side:
- catch exceptions and rethrow as custom exception
- override string conversion functions of exceptions

src/APIResponder.jl

@@ -98,7 +98,7 @@ function call_api(api::APISpec, conn::APIResponder, args, data::Dict{Symbol,Any}
         respond(conn, Nullable(api), :success, result)
     catch ex
         logerr("api_exception: ", ex)
-        respond(conn, Nullable(api), :api_exception)
+        respond(conn, Nullable(api), :api_exception, string(ex))
     end
 end
 

test/clnt.jl

@@ -61,14 +61,23 @@ function run_clnt(fmt, tport)
     println("time for $NCALLS calls to testbinary: $t secs @ $(t/NCALLS) per call")
 
     # Test Array invocation
+    println("testing array invocation...")
     resp = apicall(apiclnt, "testArray", Float64[1.0 2.0; 3.0 4.0])
     @test fnresponse(apiclnt.format, resp) == 12
 
     # Test unknown function call
+    println("testing unknown method handling...")
     resp = apicall(apiclnt, "testNoSuchMethod", Float64[1.0 2.0; 3.0 4.0])
     @test resp["code"] == 404
     resp = apicall(apiclnt, "testArray", "no such argument")
     @test resp["code"] == 500
+    @test contains(resp["data"], "MethodError")
+
+    # Test exceptions
+    println("testing server method exception handling...")
+    resp = apicall(apiclnt, "testException")
+    @test resp["code"] == 500
+    @test contains(resp["data"]["data"], "testing exception handling")
 
     close(ctx)
     close(tport)

test/srvr.jl

@@ -25,6 +25,7 @@ function run_srvr(fmt, tport, async=false, open=false)
     register(api, testbinary; resp_headers=BINARY_RESP_HDRS)
     register(api, testArray)
     register(api, testFile; resp_json=true, resp_headers=JSON_RESP_HDRS)
+    register(api, testException; resp_json=true, resp_headers=JSON_RESP_HDRS)
 
     process(api; async=async)
 end

test/srvrfn.jl

@@ -21,3 +21,5 @@ function testFile(;filename=nothing, filedata=nothing)
     #println("[", String(filedata), "]")
     string(length(filename)) * "," * string(length(filedata))
 end
+
+testException() = error("testing exception handling")