Router: Greatly improved error messages from _replicate and _active_t…

…asks

If a one-shot replication fails, you now get full info in the response
body, instead of just a "500 Internal Server Error" status.

For #1292

Source/CBLStatus.h

@@ -28,6 +28,8 @@ typedef enum {
 
     kCBLStatusServerError    = 500,
     kCBLStatusNotImplemented = 501,
+    kCBLStatusServiceUnavailable = 503,
+    kCBLStatusTimedOut       = 504,     // "Gateway Timeout"
 
     // Non-HTTP errors:
     kCBLStatusBadEncoding    = 490,

Source/CBLStatus.m

@@ -14,6 +14,7 @@
 //  and limitations under the License.
 
 #import "CBLStatus.h"
+#import "MYErrorUtils.h"
 
 
 NSString* const CBLHTTPErrorDomain = @"CBLHTTP";
@@ -99,12 +100,42 @@ BOOL CBLStatusToOutNSError(CBLStatus status, NSError** outError) {
 }
 
 
+// Mapping NSURLErrorDomain codes to CBLStatus:
+static const struct { NSInteger code; CBLStatus status; } kURLErrorToStatusMap[] = {
+    {NSURLErrorBadURL,                          kCBLStatusBadRequest},
+    {NSURLErrorUserCancelledAuthentication,     kCBLStatusUnauthorized},
+    {NSURLErrorUserAuthenticationRequired,      kCBLStatusUnauthorized},
+    {NSURLErrorCannotFindHost,                  kCBLStatusNotFound},
+    {NSURLErrorRedirectToNonExistentLocation,   kCBLStatusNotFound},
+    {NSURLErrorUnsupportedURL,                  kCBLStatusNotImplemented},
+    {NSURLErrorAppTransportSecurityRequiresSecureConnection, kCBLStatusForbidden},
+
+    {NSURLErrorResourceUnavailable,             kCBLStatusServiceUnavailable},
+    {NSURLErrorCannotConnectToHost,             kCBLStatusServiceUnavailable},
+    {NSURLErrorNetworkConnectionLost,           kCBLStatusServiceUnavailable},
+    {NSURLErrorDNSLookupFailed,                 kCBLStatusServiceUnavailable},
+    {NSURLErrorNotConnectedToInternet,          kCBLStatusServiceUnavailable},
+    {NSURLErrorNetworkConnectionLost,           kCBLStatusServiceUnavailable},
+
+    {NSURLErrorTimedOut,                        kCBLStatusTimedOut},
+    {NSURLErrorUnknown,                         kCBLStatusServerError},
+    {NSURLErrorCancelled,                       kCBLStatusCanceled},
+};
+
+
 CBLStatus CBLStatusFromNSError(NSError* error, CBLStatus defaultStatus) {
     NSInteger code = error.code;
-    if (!error)
+    if (!error) {
         return kCBLStatusOK;
-    else if ($equal(error.domain, CBLHTTPErrorDomain))
+    } else if ($equal(error.domain, CBLHTTPErrorDomain)) {
         return (CBLStatus)code;
-    else
+    } else if ($equal(error.domain, NSURLErrorDomain)) {
+        for (unsigned i=0; i < sizeof(kURLErrorToStatusMap)/sizeof(kURLErrorToStatusMap[0]); ++i) {
+            if (kURLErrorToStatusMap[i].code == code)
+                return kURLErrorToStatusMap[i].status;
+        }
+        return kCBLStatusUpstreamError;
+    } else {
         return defaultStatus;
+    }
 }

Source/CBL_Router+Handlers.m

@@ -39,6 +39,7 @@
 #import "CBLJSON.h"
 
 #import "CollectionUtils.h"
+#import "MYErrorUtils.h"
 #import "Test.h"
 
 
@@ -435,14 +436,36 @@ - (CBLStatus) do_POST_replicate {
 // subroutine of -do_POST_replicate
 - (void) replicationStopped: (NSNotification*)n {
     id<CBL_Replicator> repl = n.object;
-    _response.status = CBLStatusFromNSError(repl.error, kCBLStatusServerError);
+    NSError* error = repl.error;
+    NSDictionary* body;
+    if (error) {
+        _response.status = kCBLStatusServerError;
+        body = [self infoForReplicationError: error];
+    } else {
+        body = @{@"ok": @YES, @"session_id": repl.sessionID};
+    }
+    [self.response setBodyObject: body];
     [self sendResponseHeaders];
-    [self.response setBodyObject: $dict({@"ok", (repl.error ?nil :$true)},
-                                        {@"session_id", repl.sessionID})];
     [self sendResponseBodyAndFinish: YES];
 }
 
 
+- (NSDictionary*) infoForReplicationError: (NSError*)error {
+    if (!error)
+        return nil;
+    NSString* errorMsg;
+    CBLStatus status = CBLStatusFromNSError(error, 0);
+    if (status != 0)
+        CBLStatusToHTTPStatus(status, &errorMsg);
+    if (!errorMsg)
+        errorMsg = $sprintf(@"%@ %ld", error.domain, (long)error.code);
+    return $dict({@"error", errorMsg},
+                 {@"reason", error.localizedDescription},
+                 {@"status", (status ? @(status) : nil)},
+                 {@"url", error.my_failingURL.absoluteString});
+}
+
+
 /* CouchDB 1.2's _replicate response looks like this:
  {
     "history": [
@@ -534,10 +557,7 @@ - (NSDictionary*) activeTaskInfo: (id<CBL_Replicator>)repl {
     } else {
         status = kStatusName[repl.status];
     }
-    NSArray* error = nil;
-    NSError* errorObj = repl.error;
-    if (errorObj)
-        error = @[@(errorObj.code), errorObj.localizedDescription];
+    NSDictionary* error = [self infoForReplicationError: repl.error];
 
     NSArray* activeRequests = nil;
     if ([repl respondsToSelector: @selector(activeTasksInfo)])