img, loader: add image resizing, misc fixes

* resize images with stb_image_resize
* use tee for output handle redirection (redirectToFile blocks)
* cache original image files
* accept lseek in sandbox
* misc stbi fixes

For now, I just pulled in stb_image_resize v1. v2 is an extra 150K in
size, not sure if it's worth the cost. (Either way, we can always switch
later if needed, since the API is almost the same.)

Next step: move sixel/kitty encoders to CGI, and cache their output in
memory instead of the intermediate RGBA representation.

3 files changed, 66 insertions, 62 deletions

diff --git a/src/loader/loader.nim b/src/loader/loader.nim
index 7c76ae59..11cf714f 100644
--- a/src/loader/loader.nim
+++ b/src/loader/loader.nim
@@ -174,6 +174,16 @@ func findCachedHandle(ctx: LoaderContext; cacheId: int): LoaderHandle =
 type PushBufferResult = enum
   pbrDone, pbrUnregister
 
+proc register(ctx: LoaderContext; output: OutputHandle) =
+  assert not output.registered
+  ctx.selector.registerHandle(output.ostream.fd, {Write}, 0)
+  output.registered = true
+
+proc unregister(ctx: LoaderContext; output: OutputHandle) =
+  assert output.registered
+  ctx.selector.unregister(output.ostream.fd)
+  output.registered = false
+
 # Either write data to the target output, or append it to the list of buffers to
 # write and register the output in our selector.
 proc pushBuffer(ctx: LoaderContext; output: OutputHandle; buffer: LoaderBuffer;
@@ -203,8 +213,7 @@ proc pushBuffer(ctx: LoaderContext; output: OutputHandle; buffer: LoaderBuffer;
     if n < buffer.len:
       output.currentBuffer = buffer
       output.currentBufferIdx = n
-      ctx.selector.registerHandle(output.ostream.fd, {Write}, 0)
-      output.registered = true
+      ctx.register(output)
   else:
     output.buffers.addLast(buffer)
   pbrDone
@@ -213,8 +222,11 @@ proc getOutputId(ctx: LoaderContext): int =
   result = ctx.outputNum
   inc ctx.outputNum
 
-proc redirectToStream(ctx: LoaderContext; output: OutputHandle;
-    ps: PosixStream): bool =
+proc redirectToFile(ctx: LoaderContext; output: OutputHandle;
+    targetPath: string): bool =
+  let ps = newPosixStream(targetPath, O_CREAT or O_WRONLY, 0o600)
+  if ps == nil:
+    return false
   try:
     if output.currentBuffer != nil:
       let n = ps.sendData(output.currentBuffer, output.currentBufferIdx)
@@ -227,7 +239,7 @@ proc redirectToStream(ctx: LoaderContext; output: OutputHandle;
         ps.sclose()
         return false
   except ErrorBrokenPipe:
-    # ps or output is dead; give up.
+    # ps is dead; give up.
     ps.sclose()
     return false
   if output.istreamAtEnd:
@@ -241,13 +253,6 @@ proc redirectToStream(ctx: LoaderContext; output: OutputHandle;
     ))
   return true
 
-proc redirectToFile(ctx: LoaderContext; output: OutputHandle;
-    targetPath: string): bool =
-  let ps = newPosixStream(targetPath, O_CREAT or O_WRONLY, 0o600)
-  if ps == nil:
-    return false
-  return ctx.redirectToStream(output, ps)
-
 proc addCacheFile(ctx: LoaderContext; client: ClientData; output: OutputHandle):
     int =
   if output.parent != nil and output.parent.cacheId != -1:
@@ -326,8 +331,7 @@ proc loadStreamRegular(ctx: LoaderContext; handle, cachedHandle: LoaderHandle) =
     output.parent = nil
     let i = handle.outputs.find(output)
     if output.registered:
-      ctx.selector.unregister(output.ostream.fd)
-      output.registered = false
+      ctx.unregister(output)
     handle.outputs.del(i)
   for output in handle.outputs:
     if r == hrrBrokenPipe:
@@ -397,8 +401,8 @@ proc loadFromCache(ctx: LoaderContext; client: ClientData; handle: LoaderHandle;
   else:
     handle.sendResult(ERROR_URL_NOT_IN_CACHE)
 
-proc loadResource(ctx: LoaderContext; client: ClientData; config: LoaderClientConfig;
-    request: Request; handle: LoaderHandle) =
+proc loadResource(ctx: LoaderContext; client: ClientData;
+    config: LoaderClientConfig; request: Request; handle: LoaderHandle) =
   var redo = true
   var tries = 0
   var prevurl: URL = nil
@@ -419,16 +423,18 @@ proc loadResource(ctx: LoaderContext; client: ClientData; config: LoaderClientCo
         config.insecureSSLNoVerify, ostream)
       if handle.istream != nil:
         if ostream != nil:
-          let output = ctx.findOutput(request.body.outputId, client)
-          if output != nil:
-            if not ctx.redirectToStream(output, ostream):
-              # give up.
-              handle.rejectHandle(ERROR_FAILED_TO_REDIRECT)
-              return
+          let outputIn = ctx.findOutput(request.body.outputId, client)
+          if outputIn != nil:
+            ostream.setBlocking(false)
+            let output = outputIn.tee(ostream, ctx.getOutputId(), client.pid)
+            ctx.outputMap[ostream.fd] = output
+            output.suspended = false
+            ctx.register(output)
           else:
             ostream.sclose()
         ctx.addFd(handle)
       else:
+        assert ostream == nil
         handle.close()
     elif request.url.scheme == "stream":
       ctx.loadStream(handle, request)
@@ -538,16 +544,15 @@ proc removeClient(ctx: LoaderContext; stream: SocketStream;
     ctx.clientData.del(pid)
   stream.sclose()
 
-proc addCacheFile(ctx: LoaderContext; stream: SocketStream;
+proc addCacheFile(ctx: LoaderContext; stream: SocketStream; client: ClientData;
     r: var BufferedReader) =
   var outputId: int
   var targetPid: int
-  var sourcePid: int
   r.sread(outputId)
+  #TODO get rid of targetPid
   r.sread(targetPid)
-  r.sread(sourcePid)
-  let sourceClient = ctx.clientData[sourcePid]
-  let output = ctx.findOutput(outputId, sourceClient)
+  doAssert ctx.isPrivileged(client) or client.pid == targetPid
+  let output = ctx.findOutput(outputId, client)
   assert output != nil
   let targetClient = ctx.clientData[targetPid]
   let id = ctx.addCacheFile(targetClient, output)
@@ -613,10 +618,11 @@ proc tee(ctx: LoaderContext; stream: SocketStream; client: ClientData;
   var targetPid: int
   r.sread(sourceId)
   r.sread(targetPid)
-  let output = ctx.findOutput(sourceId, client)
-  if output != nil:
+  let outputIn = ctx.findOutput(sourceId, client)
+  if outputIn != nil:
     let id = ctx.getOutputId()
-    output.tee(stream, id, targetPid)
+    let output = outputIn.tee(stream, id, targetPid)
+    ctx.outputMap[output.ostream.fd] = output
     stream.withPacketWriter w:
       w.swrite(id)
     stream.setBlocking(false)
@@ -635,8 +641,7 @@ proc suspend(ctx: LoaderContext; stream: SocketStream; client: ClientData;
       output.suspended = true
       if output.registered:
         # do not waste cycles trying to push into output
-        output.registered = false
-        ctx.selector.unregister(output.ostream.fd)
+        ctx.unregister(output)
 
 proc resume(ctx: LoaderContext; stream: SocketStream; client: ClientData;
     r: var BufferedReader) =
@@ -646,9 +651,7 @@ proc resume(ctx: LoaderContext; stream: SocketStream; client: ClientData;
     let output = ctx.findOutput(id, client)
     if output != nil:
       output.suspended = false
-      assert not output.registered
-      output.registered = true
-      ctx.selector.registerHandle(output.ostream.fd, {Write}, 0)
+      ctx.register(output)
 
 proc equalsConstantTime(a, b: ClientKey): bool =
   static:
@@ -690,9 +693,6 @@ proc acceptConnection(ctx: LoaderContext) =
       of lcRemoveClient:
         privileged_command
         ctx.removeClient(stream, r)
-      of lcAddCacheFile:
-        privileged_command
-        ctx.addCacheFile(stream, r)
       of lcShareCachedItem:
         privileged_command
         ctx.shareCachedItem(stream, r)
@@ -708,6 +708,8 @@ proc acceptConnection(ctx: LoaderContext) =
       of lcGetCacheFile:
         privileged_command
         ctx.getCacheFile(stream, client, r)
+      of lcAddCacheFile:
+        ctx.addCacheFile(stream, client, r)
       of lcRemoveCachedItem:
         ctx.removeCachedItem(stream, client, r)
       of lcLoad:
@@ -812,8 +814,7 @@ proc handleWrite(ctx: LoaderContext; output: OutputHandle;
       unregWrite.add(output)
     else:
       # all buffers sent, no need to select on this output again for now
-      output.registered = false
-      ctx.selector.unregister(output.ostream.fd)
+      ctx.unregister(output)
 
 proc finishCycle(ctx: LoaderContext; unregRead: var seq[LoaderHandle];
     unregWrite: var seq[OutputHandle]) =
@@ -835,7 +836,7 @@ proc finishCycle(ctx: LoaderContext; unregRead: var seq[LoaderHandle];
   for output in unregWrite:
     if output.ostream != nil:
       if output.registered:
-        ctx.selector.unregister(output.ostream.fd)
+        ctx.unregister(output)
       ctx.outputMap.del(output.ostream.fd)
       output.oclose()
       let handle = output.parent
@@ -973,20 +974,14 @@ proc tee*(loader: FileLoader; sourceId, targetPid: int): (SocketStream, int) =
   r.sread(outputId)
   return (stream, outputId)
 
-# sourcePid is the PID of the output's owner. This is used in pager for images,
-# so that we can be sure that a container only loads images on the page that
-# it owns.
-proc addCacheFile*(loader: FileLoader; outputId, targetPid: int;
-    sourcePid = -1): int =
+proc addCacheFile*(loader: FileLoader; outputId, targetPid: int): int =
   let stream = loader.connect()
   if stream == nil:
     return -1
-  let sourcePid = if sourcePid == -1: loader.clientPid else: sourcePid
   stream.withLoaderPacketWriter loader, w:
     w.swrite(lcAddCacheFile)
     w.swrite(outputId)
     w.swrite(targetPid)
-    w.swrite(sourcePid)
   var r = stream.initPacketReader()
   var outputId: int
   r.sread(outputId)
@@ -1098,12 +1093,13 @@ proc doRequest*(loader: FileLoader; request: Request): Response =
     stream.sclose()
   return response
 
-proc shareCachedItem*(loader: FileLoader; id, targetPid: int) =
+proc shareCachedItem*(loader: FileLoader; id, targetPid: int; sourcePid = -1) =
   let stream = loader.connect()
   if stream != nil:
+    let sourcePid = if sourcePid != -1: sourcePid else: loader.clientPid
     stream.withLoaderPacketWriter loader, w:
       w.swrite(lcShareCachedItem)
-      w.swrite(loader.clientPid)
+      w.swrite(sourcePid)
       w.swrite(targetPid)
       w.swrite(id)
     stream.sclose()
diff --git a/src/loader/loaderhandle.nim b/src/loader/loaderhandle.nim
index 13869c8f..b1b04dee 100644
--- a/src/loader/loaderhandle.nim
+++ b/src/loader/loaderhandle.nim
@@ -108,10 +108,11 @@ proc bufferCleared*(output: OutputHandle) =
   else:
     output.currentBuffer = nil
 
-proc tee*(outputIn: OutputHandle; ostream: PosixStream; outputId, pid: int) =
-  let parent = outputIn.parent
-  parent.outputs.add(OutputHandle(
-    parent: parent,
+proc tee*(outputIn: OutputHandle; ostream: PosixStream; outputId, pid: int):
+    OutputHandle =
+  assert outputIn.suspended
+  let output = OutputHandle(
+    parent: outputIn.parent,
     ostream: ostream,
     currentBuffer: outputIn.currentBuffer,
     currentBufferIdx: outputIn.currentBufferIdx,
@@ -120,7 +121,13 @@ proc tee*(outputIn: OutputHandle; ostream: PosixStream; outputId, pid: int) =
     outputId: outputId,
     ownerPid: pid,
     suspended: outputIn.suspended
-  ))
+  )
+  when defined(debug):
+    output.url = outputIn.url
+  if outputIn.parent != nil:
+    assert outputIn.parent.parser == nil
+    outputIn.parent.outputs.add(output)
+  return output
 
 template output*(handle: LoaderHandle): OutputHandle =
   handle.outputs[0]
@@ -194,6 +201,6 @@ proc oclose*(output: OutputHandle) =
 proc close*(handle: LoaderHandle) =
   handle.iclose()
   for output in handle.outputs:
-    #TODO assert not output.registered
+    assert not output.registered
     if output.ostream != nil:
       output.oclose()
diff --git a/src/loader/response.nim b/src/loader/response.nim
index ab74571e..b8d95e36 100644
--- a/src/loader/response.nim
+++ b/src/loader/response.nim
@@ -129,6 +129,10 @@ proc onReadText(response: Response) =
       opaque.buf.setLen(olen)
       break
 
+proc resume*(response: Response) =
+  response.resumeFun(response.outputId)
+  response.resumeFun = nil
+
 proc text*(response: Response): Promise[JSResult[string]] {.jsfunc.} =
   if response.body == nil:
     let p = newPromise[JSResult[string]]()
@@ -144,8 +148,7 @@ proc text*(response: Response): Promise[JSResult[string]] {.jsfunc.} =
   response.opaque = opaque
   response.onRead = onReadText
   response.bodyUsed = true
-  response.resumeFun(response.outputId)
-  response.resumeFun = nil
+  response.resume()
   return response.bodyRead.then(proc(): JSResult[string] =
     let charset = response.getCharset(CHARSET_UTF_8)
     ok(opaque.buf.decodeAll(charset))
@@ -183,8 +186,7 @@ proc blob*(response: Response): Promise[JSResult[Blob]] {.jsfunc.} =
   response.opaque = opaque
   response.onRead = onReadBlob
   response.bodyUsed = true
-  response.resumeFun(response.outputId)
-  response.resumeFun = nil
+  response.resume()
   let contentType = response.getContentType()
   return response.bodyRead.then(proc(): JSResult[Blob] =
     let p = realloc(opaque.p, opaque.len)
@@ -220,8 +222,7 @@ proc saveToBitmap*(response: Response; bmp: Bitmap): EmptyPromise =
   response.opaque = opaque
   response.onRead = onReadBitmap
   response.bodyUsed = true
-  response.resumeFun(response.outputId)
-  response.resumeFun = nil
+  response.resume()
   return response.bodyRead
 
 proc json(ctx: JSContext; this: Response): Promise[JSResult[JSValue]]