Relaxed error handling (#471)

* Add GDB specific error classes to enable easier identification
of specific errors coming from GDB to handle them differently than other errors.
* Relax handling of errors for selected requests while running. Users cannot fix these and they often can't see them. Also, there is no good way to gracefully tell the IDE to stop a GUI update, and hence the can be considered as expected in such scenarios. 
* Skip CPU register and local variable reads while target running with aux gdb. This is to avoid expected errors in these scenarios. Neither registers nor local variables are expected to be reliably readable in this scenario.
* Relax handling of command cancelled errors when adapter is existing session. These errors are usually provoked by a command queue flush when trying to gracefully disconnect. Hence, are kind of expected and don't need to be shown to the user.
* Skip selected requests silently when debug adapter is not or no longer ready to reduce number of failing requests that can't succeed when the debug adapter is not ready yet/is no longer ready. Users can't change it, hence shouldn't be bothered with them.
* Fix incorrect stop-gdbserver-skip reason text (launch connection, not attach)
* Fix potential lockup with customResetRequest. The method wasn't sending a response if no customResetCommands
were specified. A corner case not likely to be seen by users. But it hindered adding new tests.
* Tests for relaxed error handling after disconnect

---------

Signed-off-by: Jens Reinecke <jens.reinecke@arm.com>

Author: jreineckearm

src/MIParser.ts

@@ -28,6 +28,8 @@ const DEFAULT_CHARSET = 'utf-8';
 const FIXUPS_CHARSET = new Map<string, string>([['cp65001', 'utf-8']]);
 
 export class MIParser {
+    public static readonly CMD_QUEUE_CANCELLED =
+        'MIParser command queue cancelled';
     /**
      * Encoding for GDB/MI cstring characters outside standard ASCII range.
      * Value has to match names known to TextDecoder API, see also
@@ -68,7 +70,7 @@ export class MIParser {
         entries.forEach((entry) => {
             // Call callback with error to reject command promise
             entry[1].callback('error', {
-                msg: 'MI parser command queue cancelled',
+                msg: MIParser.CMD_QUEUE_CANCELLED,
             });
             // Delete command by key
             delete this.commandQueue[entry[0]];

src/desktop/GDBTargetDebugSession.ts

@@ -31,6 +31,7 @@ import {
 import { GDBBackendFactory } from './factories/GDBBackendFactory';
 import { GDBServerFactory } from './factories/GDBServerFactory';
 import { isProcessActive } from '../util/processes';
+import { GDBCommandCancelled } from '../gdb/errors';
 
 // State of the Remote Target Debug Session
 enum SessionState {
@@ -175,6 +176,41 @@ export class GDBTargetDebugSession extends GDBDebugSession {
         };
     }
 
+    /**
+     * Checks if debug adapter is connected and ready to process debug requests
+     * driven by user interaction or other extensions.
+     *
+     * @return true if standard debug operation requests can be processed, false
+     * otherwise.
+     */
+    protected canRequestProceed(): boolean {
+        if (this.sessionInfo.state !== SessionState.SESSION_READY) {
+            return false;
+        }
+        return super.canRequestProceed();
+    }
+
+    /**
+     * Checks if an error would bring extra value to the user and if it
+     * should be reported in the debug adapter protocol response.
+     * Note: Call base class implementation last and after any explicit
+     * return of value 'true'.
+     * @param error The error to check.
+     * @return true if the error should be reported as a debug adapter protocol
+     * error response, false otherwise.
+     */
+    protected shouldReportError(error: unknown): boolean {
+        // GDBCommandCancelled occurrences for any GDB backend.
+        if (
+            error instanceof GDBCommandCancelled &&
+            this.sessionInfo.state >= SessionState.EXITING
+        ) {
+            // Exiting session, cancelling commands is expected for a graceful shutdown.
+            return false;
+        }
+        return super.shouldReportError(error);
+    }
+
     /**
      * Validate the launch/attach request arguments and throw if they contain
      * an invalid combination.
@@ -761,7 +797,7 @@ export class GDBTargetDebugSession extends GDBDebugSession {
         return new Promise((resolve, reject) => {
             if (!this.gdbserver || !isProcessActive(this.gdbserver)) {
                 const skipReason = this.launchGdbServer
-                    ? `'attach' connection`
+                    ? `'launch' connection`
                     : 'already down';
                 this.logGDBRemote(`skip stopping GDB server, ${skipReason}`);
                 resolve(false);

src/gdb/GDBBackend.ts

@@ -28,6 +28,13 @@ import { MIParser } from '../MIParser';
 import { compareVersions } from '../util/compareVersions';
 import { isProcessActive } from '../util/processes';
 import { NamedLogger } from '../namedLogger';
+import {
+    GDBPipeError,
+    GDBError,
+    GDBUnknownResponse,
+    GDBCommandCancelled,
+    GDBThreadRunning,
+} from './errors';
 
 // Expected console output for interpreter command 'show host-charset'
 // if setting is 'auto'.
@@ -333,7 +340,11 @@ export class GDBBackend extends events.EventEmitter implements IGDBBackend {
                     // Reject command on pipe error, only way to recover from potential
                     // race condition between command in flight and GDB (forced) shutdown.
                     if (error) {
-                        reject(error);
+                        const gdbError =
+                            error.message === MIParser.CMD_QUEUE_CANCELLED
+                                ? new GDBCommandCancelled(error, this.name)
+                                : new GDBPipeError(error, this.name);
+                        reject(gdbError);
                     }
                 };
                 this.parser.queueCommand(
@@ -355,7 +366,16 @@ export class GDBBackend extends events.EventEmitter implements IGDBBackend {
                                 this.logger.verbose(
                                     `GDB command: ${token} ${command} failed with '${failure.message}'`
                                 );
-                                reject(failure);
+                                // Handle messages that contain info that thread is running
+                                // Note: Move to separate function if more cases need to be handled
+                                const threadRunningRegexp =
+                                    /Selected thread is running/i;
+                                const gdbThreadRunning =
+                                    threadRunningRegexp.test(failure.message);
+                                const gdbError = gdbThreadRunning
+                                    ? new GDBThreadRunning(failure, this.name)
+                                    : new GDBError(failure, this.name);
+                                reject(gdbError);
                                 break;
                             default:
                                 failure.message = `Unknown response ${resultClass}: ${JSON.stringify(
@@ -364,7 +384,9 @@ export class GDBBackend extends events.EventEmitter implements IGDBBackend {
                                 this.logger.verbose(
                                     `GDB command: ${token} ${command} failed with unknown response '${failure.message}'`
                                 );
-                                reject(failure);
+                                reject(
+                                    new GDBUnknownResponse(failure, this.name)
+                                );
                         }
                     }
                 );