Add compile-time support for reading/writing simple streams (fixes #77)

faststreams/inputs.nim

@@ -77,6 +77,10 @@ type
   FileInputStream = ref object of InputStream
     file: File
 
+  VmInputStream = ref object of InputStream
+    data: seq[byte]
+    pos: int
+
 template Sync*(s: InputStream): InputStream = s
 
 when fsAsyncSupport:
@@ -119,6 +123,11 @@ when fsAsyncSupport:
 template makeHandle*(sp: InputStream): InputStreamHandle =
   InputStreamHandle(s: sp)
 
+proc close(s: VmInputStream) =
+  if s == nil:
+    return
+  s.pos = s.data.len
+
 proc close*(s: InputStream,
             behavior = dontWaitAsyncClose)
            {.raises: [IOError].} =
@@ -128,18 +137,21 @@ proc close*(s: InputStream,
   ## If the underlying input device requires asynchronous closing
   ## and `behavior` is set to `waitAsyncClose`, this proc will use
   ## `waitFor` to block until the async operation completes.
-  if s == nil:
-    return
+  when nimvm:
+    close(VmInputStream(s))
+  else:
+    if s == nil:
+      return
 
-  s.disconnectInputDevice()
-  s.preventFurtherReading()
-  when fsAsyncSupport:
-    if s.closeFut != nil:
-      fsTranslateErrors "Stream closing failed":
-        if behavior == waitAsyncClose:
-          waitFor s.closeFut
-        else:
-          asyncCheck s.closeFut
+    s.disconnectInputDevice()
+    s.preventFurtherReading()
+    when fsAsyncSupport:
+      if s.closeFut != nil:
+        fsTranslateErrors "Stream closing failed":
+          if behavior == waitAsyncClose:
+            waitFor s.closeFut
+          else:
+            asyncCheck s.closeFut
 
 when fsAsyncSupport:
   template close*(sp: AsyncInputStream) =
@@ -266,9 +278,12 @@ func getNewSpanOrDieTrying(s: InputStream) =
   fsAssert s.span.hasRunway
 
 func readableNow*(s: InputStream): bool =
-  if s.span.hasRunway: return true
-  getNewSpan s
-  s.span.hasRunway
+  when nimvm:
+    VmInputStream(s).pos < VmInputStream(s).data.len
+  else:
+    if s.span.hasRunway: return true
+    getNewSpan s
+    s.span.hasRunway
 
 when fsAsyncSupport:
   template readableNow*(s: AsyncInputStream): bool =
@@ -323,20 +338,26 @@ func getBestContiguousRunway(s: InputStream): Natural =
     getNewSpan s
     result = s.span.len
 
+func totalUnconsumedBytes(s: VmInputStream): Natural =
+  s.data.len - s.pos
+
 func totalUnconsumedBytes*(s: InputStream): Natural =
   ## Returns the number of bytes that are currently sitting within the stream
   ## buffers and that can be consumed with `read` or `advance`.
-  let
-    localRunway = s.span.len
-    runwayInBuffers =
-      if s.maxBufferedBytes.isSome():
-        s.maxBufferedBytes.get()
-      elif s.buffers != nil:
-        s.buffers.consumable()
-      else:
-        0
+  when nimvm:
+    totalUnconsumedBytes(VmInputStream(s))
+  else:
+    let
+      localRunway = s.span.len
+      runwayInBuffers =
+        if s.maxBufferedBytes.isSome():
+          s.maxBufferedBytes.get()
+        elif s.buffers != nil:
+          s.buffers.consumable()
+        else:
+          0
 
-  localRunway + runwayInBuffers
+    localRunway + runwayInBuffers
 
 proc prepareReadableRange(s: InputStream, rangeLen: Natural): auto =
   let
@@ -461,24 +482,34 @@ func unsafeMemoryInput*(mem: openArray[byte]): InputStreamHandle =
   ## the instance even though scope-wise, it looks like it should stay alive.
   ##
   ## See also https://github.com/nim-lang/Nim/issues/25080
-  let head = cast[ptr byte](mem)
+  when nimvm:
+    makeHandle VmInputStream(data: @mem, pos: 0)
+  else:
+    let head = cast[ptr byte](mem)
 
-  makeHandle InputStream(
-    span: PageSpan(
-      startAddr: head,
-      endAddr: offset(head, mem.len)),
-    spanEndPos: mem.len)
+    makeHandle InputStream(
+      span: PageSpan(
+        startAddr: head,
+        endAddr: offset(head, mem.len)),
+      spanEndPos: mem.len)
 
 func unsafeMemoryInput*(str: string): InputStreamHandle =
   unsafeMemoryInput str.toOpenArrayByte(0, str.len - 1)
 
+proc len(s: VmInputStream): Option[Natural] =
+  doAssert s.data.len - s.pos >= 0
+  some(Natural(s.data.len - s.pos))
+
 proc len*(s: InputStream): Option[Natural] {.raises: [IOError].} =
-  if s.vtable == nil:
-    some s.totalUnconsumedBytes
-  elif s.vtable.getLenSync != nil:
-    s.vtable.getLenSync(s)
+  when nimvm:
+    len(VmInputStream(s))
   else:
-    none Natural
+    if s.vtable == nil:
+      some s.totalUnconsumedBytes
+    elif s.vtable.getLenSync != nil:
+      s.vtable.getLenSync(s)
+    else:
+      none Natural
 
 when fsAsyncSupport:
   template len*(s: AsyncInputStream): Option[Natural] =
@@ -488,15 +519,18 @@ func memoryInput*(buffers: PageBuffers): InputStreamHandle =
   makeHandle InputStream(buffers: buffers)
 
 func memoryInput*(data: openArray[byte]): InputStreamHandle =
-  let stream = if data.len > 0:
-    let buffers = PageBuffers.init(data.len)
-    buffers.write(data)
-
-    InputStream(buffers: buffers)
+  when nimvm:
+    makeHandle VmInputStream(data: @data, pos: 0)
   else:
-    InputStream()
+    let stream = if data.len > 0:
+      let buffers = PageBuffers.init(data.len)
+      buffers.write(data)
+
+      InputStream(buffers: buffers)
+    else:
+      InputStream()
 
-  makeHandle stream
+    makeHandle stream
 
 func memoryInput*(data: openArray[char]): InputStreamHandle =
   memoryInput data.toOpenArrayByte(0, data.high())
@@ -598,8 +632,11 @@ template readable*(sp: InputStream): bool =
   # This is a template, because we want the pointer check to be
   # inlined at the call sites. Only if it fails, we call into the
   # larger non-inlined proc:
-  let s = sp
-  hasRunway(s.span) or bufferMoreDataSync(s)
+  when nimvm:
+    VmInputStream(sp).pos < VmInputStream(sp).data.len
+  else:
+    let s = sp
+    hasRunway(s.span) or bufferMoreDataSync(s)
 
 when fsAsyncSupport:
   template readable*(sp: AsyncInputStream): bool =
@@ -678,7 +715,10 @@ proc readable*(s: InputStream, n: int): bool =
   ## Just like `readable`, this operation will invoke reads on the
   ## stream input device only when necessary. See `Stream Pages`
   ## for futher discussion of this.
-  readableNImpl(s, n, noAwait, readSync)
+  when nimvm:
+    VmInputStream(s).pos + n <= VmInputStream(s).data.len
+  else:
+    readableNImpl(s, n, noAwait, readSync)
 
 when fsAsyncSupport:
   template readable*(sp: AsyncInputStream, np: int): bool =
@@ -691,13 +731,20 @@ when fsAsyncSupport:
 
     readableNImpl(s, n, fsAwait, readAsync)
 
+template peek(s: VmInputStream): byte =
+  doAssert s.pos < s.data.len
+  s.data[s.pos]
+
 template peek*(sp: InputStream): byte =
-  let s = sp
-  if hasRunway(s.span):
-    s.span.startAddr[]
+  when nimvm:
+    peek(VmInputStream(sp))
   else:
-    getNewSpanOrDieTrying s
-    s.span.startAddr[]
+    let s = sp
+    if hasRunway(s.span):
+      s.span.startAddr[]
+    else:
+      getNewSpanOrDieTrying s
+      s.span.startAddr[]
 
 when fsAsyncSupport:
   template peek*(s: AsyncInputStream): byte =
@@ -707,42 +754,64 @@ func readFromNewSpan(s: InputStream): byte =
   getNewSpanOrDieTrying s
   s.span.read()
 
+template read(s: VmInputStream): byte =
+  doAssert s.pos < s.data.len
+  inc s.pos
+  s.data[s.pos-1]
+
 template read*(sp: InputStream): byte =
-  let s = sp
-  if hasRunway(s.span):
-    s.span.read()
+  when nimvm:
+    read(VmInputStream(sp))
   else:
-    readFromNewSpan s
+    let s = sp
+    if hasRunway(s.span):
+      s.span.read()
+    else:
+      readFromNewSpan s
 
 when fsAsyncSupport:
   template read*(s: AsyncInputStream): byte =
     read InputStream(s)
 
+func peekAt(s: VmInputStream, pos: int): byte =
+  doAssert s.pos + pos < s.data.len
+  s.data[s.pos + pos]
+
 func peekAt*(s: InputStream, pos: int): byte {.inline.} =
-  let runway = s.span.len
-  if pos < runway:
-    let peekHead = offset(s.span.startAddr, pos)
-    return peekHead[]
+  when nimvm:
+    return peekAt(VmInputStream(s), pos)
+  else:
+    let runway = s.span.len
+    if pos < runway:
+      let peekHead = offset(s.span.startAddr, pos)
+      return peekHead[]
 
-  if s.buffers != nil:
-    var p = pos - runway
-    for page in s.buffers.queue:
-      if p < page.len():
-        return page.data()[p]
-      p -= page.len()
+    if s.buffers != nil:
+      var p = pos - runway
+      for page in s.buffers.queue:
+        if p < page.len():
+          return page.data()[p]
+        p -= page.len()
 
-  fsAssert false,
-    "peeking past readable position pos=" & $pos & " readable = " & $s.totalUnconsumedBytes()
+    fsAssert false,
+      "peeking past readable position pos=" & $pos & " readable = " & $s.totalUnconsumedBytes()
 
 when fsAsyncSupport:
   template peekAt*(s: AsyncInputStream, pos: int): byte =
     peekAt InputStream(s), pos
 
+func advance(s: VmInputStream) =
+  doAssert s.pos < s.data.len
+  inc s.pos
+
 func advance*(s: InputStream) =
-  if s.span.atEnd:
-    getNewSpanOrDieTrying s
+  when nimvm:
+    advance(VmInputStream(s))
+  else:
+    if s.span.atEnd:
+      getNewSpanOrDieTrying s
 
-  s.span.advance()
+    s.span.advance()
 
 func advance*(s: InputStream, n: Natural) =
   # TODO This is silly, implement it properly
@@ -813,19 +882,31 @@ template readIntoExImpl(s: InputStream,
 
   dstLen - bytesDeficit
 
+proc readIntoEx(s: VmInputStream, dst: var openArray[byte]): int =
+  result = 0
+  for i in 0 ..< dst.len:
+    if s.pos >= s.data.len:
+      break
+    dst[i] = s.data[s.pos]
+    inc s.pos
+    inc result
+
 proc readIntoEx*(s: InputStream, dst: var openArray[byte]): int =
   ## Read data into the destination buffer.
   ##
   ## Returns the number of bytes that were successfully
   ## written to the buffer. The function will return a
   ## number smaller than the buffer length only if EOF
   ## was reached before the buffer was fully populated.
-  if dst.len > 0:
-    let dstAddr = baseAddr dst
-    let dstLen = dst.len
-    readIntoExImpl(s, dstAddr, dstLen, noAwait, readSync)
+  when nimvm:
+    readIntoEx(VmInputStream(s), dst)
   else:
-    0
+    if dst.len > 0:
+      let dstAddr = baseAddr dst
+      let dstLen = dst.len
+      readIntoExImpl(s, dstAddr, dstLen, noAwait, readSync)
+    else:
+      0
 
 proc readInto*(s: InputStream, target: var openArray[byte]): bool =
   ## Read data into the destination buffer.
@@ -900,15 +981,25 @@ template readNImpl(sp: InputStream,
 
   makeOpenArray(startAddr, n)
 
+template read(s: VmInputStream, n: Natural): openArray[byte] =
+  doAssert s.pos + n - 1 <= s.data.len, "not enough data to read"
+  toOpenArray(s.data, s.pos, s.pos + n - 1)
+
 template read*(sp: InputStream, np: static Natural): openArray[byte] =
-  const n = np
-  when n < maxStackUsage:
-    readNImpl(sp, n, MemAllocType.StackMem)
+  when nimvm:
+    read(VmInputStream(sp), np)
   else:
-    readNImpl(sp, n, MemAllocType.HeapMem)
+    const n = np
+    when n < maxStackUsage:
+      readNImpl(sp, n, MemAllocType.StackMem)
+    else:
+      readNImpl(sp, n, MemAllocType.HeapMem)
 
 template read*(s: InputStream, n: Natural): openArray[byte] =
-  readNImpl(s, n, MemAllocType.HeapMem)
+  when nimvm:
+    read(VmInputStream(s), n)
+  else:
+    readNImpl(s, n, MemAllocType.HeapMem)
 
 when fsAsyncSupport:
   template read*(s: AsyncInputStream, n: Natural): openArray[byte] =
@@ -938,7 +1029,10 @@ when fsAsyncSupport:
       none byte
 
 func pos*(s: InputStream): int {.inline.} =
-  s.spanEndPos - s.span.len
+  when nimvm:
+    VmInputStream(s).pos
+  else:
+    s.spanEndPos - s.span.len
 
 when fsAsyncSupport:
   template pos*(s: AsyncInputStream): int =