sasjs · allanbowe · Jul 15, 2026 · Jul 15, 2026
diff --git a/api/docs/diagrams/code-execution-overview.md b/api/docs/diagrams/code-execution-overview.md
@@ -30,8 +30,9 @@ fresh per request inside `processProgram`.
   code into the session and drives it to completion/failure, per runtime.
 - `api/src/controllers/internal/Execution.ts` — `ExecutionController`,
   the entry point controllers call; acquires a session, calls
-  `processProgram`, reads back `log.log`/`webout.txt`/headers, builds the
-  HTTP response (or a `SessionExecutionError` on failure).
+  `processProgram`, reads back `log.log`/`webout.txt`/headers, and builds
+  the HTTP response. A failed session (any runtime) is embedded in that
+  same response, not thrown as a separate error.
 - `api/src/controllers/internal/create{SAS,JS,Python,R}Program.ts` —
   per-runtime code templating (wraps the user's submitted code with
   boilerplate: variable injection, `_webout` redirection, etc).

diff --git a/api/docs/diagrams/request-execution-flow.md b/api/docs/diagrams/request-execution-flow.md
@@ -8,7 +8,7 @@ fresh interpreter process per request).
 ```mermaid
 flowchart TD
     A["HTTP request<br/>POST /SASjsApi/code/execute<br/>or /SASjsApi/stp/execute"] --> B["Controller<br/>code.ts / stp.ts<br/>try/catch wrapper"]
-    B --> C["ExecutionController.executeProgram<br/>or .executeFile<br/>Execution.ts:58-91"]
+    B --> C["ExecutionController.executeProgram<br/>or .executeFile<br/>Execution.ts:40-77"]
     C --> D{"session already provided?<br/>(e.g. file-upload flow)"}
     D -- no --> E["getSessionController(runTime).getSession()<br/>Session.ts:59-69"]
     D -- yes --> F["use provided session"]
@@ -18,30 +18,28 @@ flowchart TD
     H --> J["pre-warm: if pool has fewer<br/>than 3 pending, fire off more<br/>createSession() calls (not awaited)<br/>Session.ts:66"]
     I --> J
     F --> K
-    J --> K["session.state = running<br/>Execution.ts:96"]
-    K --> L["write webout.txt (empty),<br/>reqHeaders.txt<br/>Execution.ts:103-107"]
-    L --> M["processProgram(...)<br/>processProgram.ts:16-27"]
+    J --> K["session.state = running<br/>Execution.ts:78"]
+    K --> L["write webout.txt (empty),<br/>reqHeaders.txt<br/>Execution.ts:85-89"]
+    L --> M["processProgram(...)<br/>Execution.ts:96-107"]
 
     M --> N{"runTime?"}
 
     N -- SAS --> O["createSASProgram():<br/>wrap user code with _webout<br/>filename, macro vars, autoexec"]
     O --> P["write code.sas via .bkp + rename<br/>processProgram.ts:48-49"]
-    P --> Q["poll: while session.state !== completed<br/>processProgram.ts:52-58"]
-    Q -- "state becomes completed" --> R["resolve"]
-    Q -- "state becomes failed" --> S["throw Error(session.failureReason)"]
+    P --> Q["poll: while state !== completed<br/>AND state !== failed<br/>processProgram.ts:58-63"]
+    Q --> R["processProgram() resolves either way -<br/>state was set by the session's own<br/>process exit handler in Session.ts,<br/>see sas-execution-handshake.md"]
 
     N -- "JS / PY / R" --> T["createJSProgram / createPythonProgram /<br/>createRProgram: wrap user code similarly"]
-    T --> U["write code file; spawn interpreter<br/>fresh via execFile; pipe stdout/stderr<br/>into a log.log write stream<br/>processProgram.ts:108-134"]
-    U -- "exit 0" --> R
-    U -- "exit non-zero" --> S
+    T --> U["write code file; spawn interpreter<br/>fresh via execFile; pipe stdout/stderr<br/>into a log.log write stream<br/>processProgram.ts:117-124"]
+    U -- "exit 0" --> Uc["session.state = completed<br/>processProgram.ts:126"]
+    U -- "exit non-zero" --> Uf["session.state = failed<br/>session.failureReason = err.toString()<br/>processProgram.ts:131-133"]
+    Uc --> R
+    Uf --> R
 
-    R --> V["read log.log, webout.txt,<br/>stpsrv_header.txt<br/>Execution.ts:128-131"]
-    V --> W["build httpHeaders + result<br/>return ExecuteReturnRaw<br/>Execution.ts:128-151"]
-    W --> X["Controller: res.send(result)<br/>HTTP 200"]
-
-    S --> Y["catch in Execution.ts:109-126:<br/>read whatever log exists,<br/>throw SessionExecutionError(message, log)"]
-    Y --> Z["Controller catch block<br/>rethrow { code: 400, status: 'failure',<br/>message, error, log }"]
-    Z --> AA["res.status(err.code).send(err)<br/>HTTP 400 with complete log"]
+    R --> V["read log.log, webout.txt,<br/>stpsrv_header.txt<br/>Execution.ts:109-113, 121-125"]
+    V --> W["guard: if state !== failed,<br/>set state = completed<br/>(don't overwrite a failed session)<br/>Execution.ts:127-137"]
+    W --> X["build httpHeaders + result;<br/>embed log in result if<br/>isDebugOn(vars) or<br/>session.failureReason is set<br/>Execution.ts:139-164"]
+    X --> Y["Controller: res.send(result)<br/>HTTP 200<br/>(log embedded if the session failed -<br/>same shape as a successful run)"]
 ```
 
 ## Notes
@@ -55,9 +53,16 @@ flowchart TD
   `failed` either way, and both paths flow through the same log/webout
   reading logic in `Execution.ts` afterward. The mechanics of *how* that
   state gets set differ substantially (see `session-lifecycle.md`).
+- **A failed session never throws.** `processProgram()` resolves normally
+  whether the session completed or failed - a failed session (e.g. SAS
+  `%abort;`, or a non-zero JS/PY/R exit) is a normal outcome of running
+  arbitrary user code, not a request-shape/server problem. There is no
+  separate error path: the same `Execution.ts:139-164` logic that embeds
+  the log for a debug-mode successful run also embeds it when
+  `session.failureReason` is set, and the controller always responds 200.
 - **`includePrintOutput`** (SAS only) additionally appends `output.lst`
   content to the result when debug mode is on - omitted above for brevity;
-  see `Execution.ts:135-142`.
+  see `Execution.ts:149-156`.
 - **`triggerProgram`/`triggerCode`** (fire-and-forget variants, not shown)
   call the same `ExecutionController` methods without awaiting them and
   immediately return `{ sessionId }`; the client polls

diff --git a/api/docs/diagrams/sas-execution-handshake.md b/api/docs/diagrams/sas-execution-handshake.md
@@ -33,9 +33,9 @@ sequenceDiagram
     Client->>Ctrl: POST .../execute { code, runTime: sas }
     Ctrl->>Exec: executeProgram({ program, runTime: SAS, ... })
     Exec->>Pool: getSession() returns the pending session (Session.ts:59-69)
-    Exec->>Exec: session.state = running (Execution.ts:96)
-    Exec->>FS: createFile(webout.txt, "") and createFile(reqHeaders.txt, ...) (Execution.ts:103-107)
-    Exec->>Pool: processProgram(program, session, ...) (Execution.ts:110-121)
+    Exec->>Exec: session.state = running (Execution.ts:78)
+    Exec->>FS: createFile(webout.txt, "") and createFile(reqHeaders.txt, ...) (Execution.ts:85-89)
+    Exec->>Pool: processProgram(program, session, ...) (Execution.ts:96-107)
     Pool->>FS: createSASProgram() wraps user code with macro vars,<br/>_webout filename, autoexec injection (createSASProgram.ts)
     Pool->>FS: write code.sas.bkp, then rename to code.sas (processProgram.ts:48-49)
     Note over FS: write-then-rename, not a direct write,<br/>so SAS never reads a partial file
@@ -45,24 +45,24 @@ sequenceDiagram
     Note over SAS: -SYSIN has pointed at code.sas from the start,<br/>so SAS now executes ITS CONTENT as the main job
     SAS->>FS: writes log.log, output.lst, webout.txt while running
 
-    Pool->>Pool: processProgram poll loop:<br/>while session.state !== completed (processProgram.ts:52-58)
+    Pool->>Pool: processProgram poll loop:<br/>while state !== completed AND state !== failed (processProgram.ts:58-63)
 
     alt program reaches EOF normally
         SAS->>SAS: exits with code 0
         SAS-->>Pool: execFilePromise resolves - .then() (Session.ts:148-152)
         Pool->>Pool: session.state = completed
-        Pool-->>Exec: processProgram() resolves
-    else program aborts (fatal error, license failure, hard STOP)
+    else program aborts (e.g. %abort, fatal error, license failure, hard STOP)
         SAS->>SAS: exits with non-zero code
         SAS-->>Pool: execFilePromise rejects - .catch() (Session.ts:153-163)
         Pool->>Pool: session.state = failed<br/>session.failureReason = err.toString()
-        Pool-->>Exec: processProgram() throws (processProgram.ts:53-55)
     end
     deactivate SAS
+    Note over Pool,Exec: either way processProgram() just RESOLVES here -<br/>a failed session is a normal outcome of running user<br/>code, not a request-shape/server problem, so it never throws<br/>(processProgram.ts:58-63, same as the JS/PY/R branch below)
 
-    Exec->>FS: read log.log, webout.txt, stpsrv_header.txt (Execution.ts:123, 128-131)
-    Exec-->>Ctrl: { httpHeaders, result }<br/>or throws SessionExecutionError{ message, log } (Execution.ts:109-126)
-    Ctrl-->>Client: 200 + result<br/>or 400 { status, message, error, log }
+    Exec->>FS: read log.log, webout.txt, stpsrv_header.txt (Execution.ts:109-112, 121-125)
+    Note over Exec: if session.failureReason is set, the log is folded into<br/>result the same way isDebugOn(vars) already does for a<br/>successful run - no separate error shape (Execution.ts:158-164)
+    Exec-->>Ctrl: { httpHeaders, result }
+    Ctrl-->>Client: 200 + result<br/>(log embedded in result if the session failed)
 ```
 
 ## Why this design

diff --git a/api/docs/diagrams/session-lifecycle.md b/api/docs/diagrams/session-lifecycle.md
@@ -14,10 +14,10 @@ stateDiagram-v2
     initialising --> pending: dummy SYSIN file deleted<br/>by SAS's autoexec<br/>waitForSession(), Session.ts:175-192
     initialising --> failed: spawned SAS process exits<br/>before handshake completes<br/>Session.ts:153-163, 184-188
 
-    pending --> running: session picked for a request<br/>executeProgram(), Execution.ts:94-96
+    pending --> running: session picked for a request<br/>executeProgram(), Execution.ts:76-78
 
-    running --> completed: process exits 0<br/>SAS: Session.ts:148-152 (original process)<br/>JS/PY/R: processProgram.ts:116-120 (fresh process)
-    running --> failed: process exits non-zero<br/>SAS: Session.ts:153-163<br/>JS/PY/R: processProgram.ts:121-131<br/>failureReason = err.toString()
+    running --> completed: process exits 0<br/>SAS: Session.ts:148-152 (original process)<br/>JS/PY/R: processProgram.ts:124-129 (fresh process)
+    running --> failed: process exits non-zero<br/>SAS: Session.ts:153-163<br/>JS/PY/R: processProgram.ts:130-135<br/>failureReason = err.toString()<br/>neither branch throws - see request-execution-flow.md
 
     completed --> [*]: deleteSession()<br/>scheduleSessionDestroy(), Session.ts:194-236
     failed --> [*]: deleteSession()<br/>scheduleSessionDestroy()
@@ -55,7 +55,7 @@ stateDiagram-v2
 | Reader | Location | Watches for |
 |---|---|---|
 | `waitForSession` | `Session.ts:175-192` | `failed` (breaks early) or the dummy SYSIN file disappearing (implies session survived init) |
-| `processProgram` (SAS branch poll loop) | `processProgram.ts:52-58` | `completed` (success exit) or `failed` (throws, carrying `session.failureReason`) |
+| `processProgram` (SAS branch poll loop) | `processProgram.ts:58-63` | `completed` or `failed` - either just stops the loop and returns normally; `failed` does **not** throw. `Execution.ts` reads `session.failureReason` afterward to fold the log into a normal (200) result, same as it already does for JS/PY/R. |
 | `scheduleSessionDestroy` | `Session.ts:204-236` | `running` (extends death timer instead of destroying) |
 
 ## Asymmetry between runtimes
@@ -65,6 +65,13 @@ stateDiagram-v2
   `running`/`completed`/`failed` are all driven by that *same* process's
   eventual exit.
 - **JS/PY/R**: a session is cheap (folder + id, no process). The interpreter
-  process is spawned fresh, per request, inside `processProgram.ts:115` and
+  process is spawned fresh, per request, inside `processProgram.ts:124` and
   its exit drives `completed`/`failed` directly in the same function - there
-  is no separate poll loop for these runtimes.
+  is no separate poll loop for these runtimes (SAS needs one because it's
+  polling a state change happening in a process spawned earlier, at session
+  creation; JS/PY/R just `await` the process they spawn right there).
+- **Both runtimes resolve `processProgram()` normally on `failed`, they
+  never throw for it** - a failed session (any runtime) is a normal outcome
+  of running arbitrary user code, not a request-shape/server problem. See
+  `request-execution-flow.md` for how `Execution.ts` turns that into a
+  response.
diff --git a/api/src/controllers/code.ts b/api/src/controllers/code.ts
@@ -114,8 +114,7 @@ const executeCode = async (
       code: 400,
       status: 'failure',
       message: 'Job execution failed.',
-      error: typeof err === 'object' ? err.toString() : err,
-      log: err?.log
+      error: typeof err === 'object' ? err.toString() : err
     }
   }
 }

diff --git a/api/src/controllers/internal/Execution.ts b/api/src/controllers/internal/Execution.ts
@@ -15,24 +15,6 @@ export interface ExecutionVars {
   [key: string]: string | number | undefined
 }
 
-// Thrown when the session itself fails (e.g. SAS exits abnormally via
-// %abort;). Carries the complete log - by the time this is thrown, the
-// session's process has already exited, so the log file it wrote is final,
-// not a partial/truncated snapshot.
-export class SessionExecutionError extends Error {
-  constructor(
-    message: string,
-    public log?: string
-  ) {
-    super(message)
-
-    // required for `instanceof` to work when compiling to ES5, since the
-    // default __extends helper does not preserve the prototype chain for
-    // classes extending built-ins like Error
-    Object.setPrototypeOf(this, SessionExecutionError.prototype)
-  }
-}
-
 export interface ExecuteReturnRaw {
   httpHeaders: HTTPHeaders
   result: string | Buffer
@@ -106,24 +88,23 @@ export class ExecutionController {
       preProgramVariables?.httpHeaders.join('\n') ?? ''
     )
 
-    try {
-      await processProgram(
-        program,
-        preProgramVariables,
-        vars,
-        session,
-        weboutPath,
-        headersPath,
-        tokenFile,
-        runTime,
-        logPath,
-        otherArgs
-      )
-    } catch (err: any) {
-      const log = (await fileExists(logPath)) ? await readFile(logPath) : ''
-
-      throw new SessionExecutionError(err.message, log)
-    }
+    // A failed session (e.g. SAS via %abort;, or a non-zero JS/PY/R exit)
+    // is a normal outcome of running arbitrary user code, not a
+    // request-shape/server problem - processProgram resolves rather than
+    // throwing in that case, and the session.failureReason check below
+    // folds the log into the same result shape a successful run returns.
+    await processProgram(
+      program,
+      preProgramVariables,
+      vars,
+      session,
+      weboutPath,
+      headersPath,
+      tokenFile,
+      runTime,
+      logPath,
+      otherArgs
+    )
 
     const log = (await fileExists(logPath)) ? await readFile(logPath) : ''
     const headersContent = (await fileExists(headersPath))

diff --git a/api/src/controllers/internal/processProgram.ts b/api/src/controllers/internal/processProgram.ts
@@ -48,12 +48,17 @@ export const processProgram = async (
     await createFile(codePath + '.bkp', program)
     await moveFile(codePath + '.bkp', codePath)
 
-    // we now need to poll the session status
-    while (session.state !== SessionState.completed) {
-      if (session.state === SessionState.failed) {
-        throw new Error(session.failureReason || 'SAS session failed')
-      }
-
+    // we now need to poll the session status. A failed session (e.g. from
+    // %abort;) is not a request-shape/server problem - it's a normal
+    // outcome of running arbitrary user code, same as a SAS ERROR: in the
+    // log without %abort;. So we just stop polling rather than throwing;
+    // Execution.ts already knows how to turn session.failureReason into a
+    // 200 response with the log embedded, matching how JS/PY/R (the else
+    // branch below) has always handled a failed session.
+    while (
+      session.state !== SessionState.completed &&
+      session.state !== SessionState.failed
+    ) {
       await delay(50)
     }
   } else {

diff --git a/api/src/controllers/internal/spec/Execution.spec.ts b/api/src/controllers/internal/spec/Execution.spec.ts
@@ -2,7 +2,7 @@ import path from 'path'
 import os from 'os'
 import { createFile, deleteFolder, generateTimestamp } from '@sasjs/utils'
 import * as ProcessProgramModule from '../processProgram'
-import { ExecutionController, SessionExecutionError } from '../Execution'
+import { ExecutionController } from '../Execution'
 import { Session, SessionState, PreProgramVars } from '../../../types'
 import { RunTimeType } from '../../../utils'
 
@@ -83,8 +83,15 @@ describe('ExecutionController.executeProgram', () => {
     })
   })
 
+  // A failed SAS session (e.g. from %abort;) is a normal outcome of
+  // running arbitrary user code, not a request-shape/server problem - the
+  // same way a plain SAS ERROR: in the log (without %abort;) already
+  // returns 200 with the log embedded. This mirrors the JS/PY/R failure
+  // path above: resolve normally, don't throw, and let the existing
+  // session.failureReason check below produce the same result shape as a
+  // successful run.
   describe('SAS failure path', () => {
-    it('throws a SessionExecutionError carrying the complete log when the session fails', async () => {
+    it('returns the complete log embedded in a normal result instead of throwing, when the session fails', async () => {
       const logPath = path.join(session.path, 'log.log')
       const logContent =
         'NOTE: SAS session\nERROR: SAS session terminated. See log for details.\n'
@@ -94,24 +101,26 @@ describe('ExecutionController.executeProgram', () => {
       jest
         .spyOn(ProcessProgramModule, 'processProgram')
         .mockImplementation(async () => {
-          throw new Error('ERROR: SAS session terminated. See log for details.')
+          // mirrors the real SAS branch after the fix: sets
+          // state/failureReason and resolves, exactly like the JS/PY/R
+          // branch already does - it does not throw
+          session.state = SessionState.failed
+          session.failureReason =
+            'ERROR: SAS session terminated. See log for details.'
         })
 
       const controller = new ExecutionController()
 
-      const resultPromise = controller.executeProgram({
+      const { result } = await controller.executeProgram({
         program: '%abort;',
         preProgramVariables,
         vars: {},
         session,
         runTime: RunTimeType.SAS
       })
 
-      await expect(resultPromise).rejects.toBeInstanceOf(SessionExecutionError)
-      await expect(resultPromise).rejects.toMatchObject({
-        log: logContent,
-        message: expect.stringContaining('SAS session terminated')
-      })
+      expect(session.state).toBe(SessionState.failed)
+      expect(result).toEqual(expect.stringContaining(logContent))
     })
   })
 })
diff --git a/api/src/controllers/internal/spec/processProgram.spec.ts b/api/src/controllers/internal/spec/processProgram.spec.ts
@@ -65,7 +65,13 @@ describe('processProgram (SAS runtime)', () => {
     await deleteFolder(session.path)
   })
 
-  it('rejects instead of hanging when the session fails (e.g. %abort;)', async () => {
+  it('resolves instead of hanging when the session fails (e.g. %abort;)', async () => {
+    // mirrors the JS/PY/R branch below: a session failure is a normal
+    // outcome of running arbitrary user code (like a SAS ERROR: in the
+    // log without %abort;), not a server-side/request-shape problem - so
+    // processProgram must not throw here, just stop polling. Execution.ts
+    // is responsible for turning session.failureReason into a 200 response
+    // with the log embedded, the same way it already does for JS/PY/R.
     setTimeout(() => {
       session.state = SessionState.failed
       session.failureReason =
@@ -84,7 +90,7 @@ describe('processProgram (SAS runtime)', () => {
         RunTimeType.SAS,
         logPath
       )
-    ).rejects.toThrow(/SAS session terminated/)
+    ).resolves.toBeUndefined()
   }, 3000)
 
   it('resolves without throwing when the session completes normally', async () => {

diff --git a/api/src/controllers/stp.ts b/api/src/controllers/stp.ts
@@ -166,8 +166,7 @@ const execute = async (
       code: 400,
       status: 'failure',
       message: 'Job execution failed.',
-      error: typeof err === 'object' ? err.toString() : err,
-      log: err?.log
+      error: typeof err === 'object' ? err.toString() : err
     }
   }
 }