[#24789][prism] internal/coders.go and tests (#25476)

* [prism] coders + initial test file.

* [prism] internal/coders.go

* [prism] finish coder coverage

* [prism] no-alloc doc

* review commit

---------

Co-authored-by: lostluck <[email protected]>

sdks/go/pkg/beam/runners/prism/internal/coders.go

@@ -0,0 +1,243 @@
+// Licensed to the Apache Software Foundation (ASF) under one or more
+// contributor license agreements.  See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership.
+// The ASF licenses this file to You under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with
+// the License.  You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/graph/coder"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/runtime/exec"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/util/ioutilx"
+	pipepb "github.com/apache/beam/sdks/v2/go/pkg/beam/model/pipeline_v1"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/runners/prism/internal/urns"
+	"golang.org/x/exp/slog"
+	"google.golang.org/protobuf/encoding/prototext"
+)
+
+// leafCoders lists coder urns the runner knows how to manipulate.
+// In particular, ones that won't be a problem to parse, in general
+// because they have a known total size.
+var leafCoders = map[string]struct{}{
+	urns.CoderBytes:          {},
+	urns.CoderStringUTF8:     {},
+	urns.CoderLengthPrefix:   {},
+	urns.CoderVarInt:         {},
+	urns.CoderDouble:         {},
+	urns.CoderBool:           {},
+	urns.CoderGlobalWindow:   {},
+	urns.CoderIntervalWindow: {},
+}
+
+func isLeafCoder(c *pipepb.Coder) bool {
+	_, ok := leafCoders[c.GetSpec().GetUrn()]
+	return ok
+}
+
+// makeWindowedValueCoder gets the coder for the PCollection, renders it safe, and adds it to the coders map.
+//
+// PCollection coders are not inherently WindowValueCoder wrapped, and they are added by the runner
+// for crossing the FnAPI boundary at data sources and data sinks.
+func makeWindowedValueCoder(pID string, comps *pipepb.Components, coders map[string]*pipepb.Coder) string {
+	col := comps.GetPcollections()[pID]
+	cID := lpUnknownCoders(col.GetCoderId(), coders, comps.GetCoders())
+	wcID := comps.GetWindowingStrategies()[col.GetWindowingStrategyId()].GetWindowCoderId()
+
+	// The runner needs to be defensive, and tell the SDK to Length Prefix
+	// any coders that it doesn't understand.
+	// So here, we look at the coder and its components, and produce
+	// new coders that we know how to deal with.
+
+	// Produce ID for the Windowed Value Coder
+	wvcID := "cwv_" + pID
+	wInC := &pipepb.Coder{
+		Spec: &pipepb.FunctionSpec{
+			Urn: urns.CoderWindowedValue,
+		},
+		ComponentCoderIds: []string{cID, wcID},
+	}
+	// Populate the coders to send with the new windowed value coder.
+	coders[wvcID] = wInC
+	return wvcID
+}
+
+// makeWindowCoders makes the coder pair but behavior is ultimately determined by the strategy's windowFn.
+func makeWindowCoders(wc *pipepb.Coder) (exec.WindowDecoder, exec.WindowEncoder) {
+	var cwc *coder.WindowCoder
+	switch wc.GetSpec().GetUrn() {
+	case urns.CoderGlobalWindow:
+		cwc = coder.NewGlobalWindow()
+	case urns.CoderIntervalWindow:
+		cwc = coder.NewIntervalWindow()
+	default:
+		slog.Log(slog.LevelError, "makeWindowCoders: unknown urn", slog.String("urn", wc.GetSpec().GetUrn()))
+		panic(fmt.Sprintf("makeWindowCoders, unknown urn: %v", prototext.Format(wc)))
+	}
+	return exec.MakeWindowDecoder(cwc), exec.MakeWindowEncoder(cwc)
+}
+
+// lpUnknownCoders takes a coder, and populates coders with any new coders
+// coders that the runner needs to be safe, and speedy.
+// It returns either the passed in coder id, or the new safe coder id.
+func lpUnknownCoders(cID string, bundle, base map[string]*pipepb.Coder) string {
+	// First check if we've already added the LP version of this coder to coders already.
+	lpcID := cID + "_lp"
+	// Check if we've done this one before.
+	if _, ok := bundle[lpcID]; ok {
+		return lpcID
+	}
+	// All coders in the coders map have been processed.
+	if _, ok := bundle[cID]; ok {
+		return cID
+	}
+	// Look up the canonical location.
+	c, ok := base[cID]
+	if !ok {
+		// We messed up somewhere.
+		panic(fmt.Sprint("unknown coder id:", cID))
+	}
+	// Add the original coder to the coders map.
+	bundle[cID] = c
+	// If we don't know this coder, and it has no sub components,
+	// we must LP it, and we return the LP'd version.
+	leaf := isLeafCoder(c)
+	if len(c.GetComponentCoderIds()) == 0 && !leaf {
+		lpc := &pipepb.Coder{
+			Spec: &pipepb.FunctionSpec{
+				Urn: urns.CoderLengthPrefix,
+			},
+			ComponentCoderIds: []string{cID},
+		}
+		bundle[lpcID] = lpc
+		return lpcID
+	}
+	// We know we have a composite, so if we count this as a leaf, move everything to
+	// the coders map.
+	if leaf {
+		// Copy the components from the base.
+		for _, cc := range c.GetComponentCoderIds() {
+			bundle[cc] = base[cc]
+		}
+		return cID
+	}
+	var needNewComposite bool
+	var comps []string
+	for _, cc := range c.GetComponentCoderIds() {
+		rcc := lpUnknownCoders(cc, bundle, base)
+		if cc != rcc {
+			needNewComposite = true
+		}
+		comps = append(comps, rcc)
+	}
+	if needNewComposite {
+		lpc := &pipepb.Coder{
+			Spec:              c.GetSpec(),
+			ComponentCoderIds: comps,
+		}
+		bundle[lpcID] = lpc
+		return lpcID
+	}
+	return cID
+}
+
+// reconcileCoders ensures that the bundle coders are primed with initial coders from
+// the base pipeline components.
+func reconcileCoders(bundle, base map[string]*pipepb.Coder) {
+	for {
+		var comps []string
+		for _, c := range bundle {
+			for _, ccid := range c.GetComponentCoderIds() {
+				if _, ok := bundle[ccid]; !ok {
+					// We don't have the coder yet, so in we go.
+					comps = append(comps, ccid)
+				}
+			}
+		}
+		if len(comps) == 0 {
+			return
+		}
+		for _, ccid := range comps {
+			c, ok := base[ccid]
+			if !ok {
+				panic(fmt.Sprintf("unknown coder id during reconciliation: %v", ccid))
+			}
+			bundle[ccid] = c
+		}
+	}
+}
+
+// pullDecoder return a function that will extract the bytes
+// for the associated coder. Uses a buffer and a TeeReader to extract the original
+// bytes from when decoding elements.
+func pullDecoder(c *pipepb.Coder, coders map[string]*pipepb.Coder) func(io.Reader) []byte {
+	dec := pullDecoderNoAlloc(c, coders)
+	return func(r io.Reader) []byte {
+		var buf bytes.Buffer
+		tr := io.TeeReader(r, &buf)
+		dec(tr)
+		return buf.Bytes()
+	}
+}
+
+// pullDecoderNoAlloc returns a function that decodes a single eleemnt of the given coder.
+// Intended to only be used as an internal function for pullDecoder, which will use a io.TeeReader
+// to extract the bytes.
+func pullDecoderNoAlloc(c *pipepb.Coder, coders map[string]*pipepb.Coder) func(io.Reader) {
+	urn := c.GetSpec().GetUrn()
+	switch urn {
+	// Anything length prefixed can be treated as opaque.
+	case urns.CoderBytes, urns.CoderStringUTF8, urns.CoderLengthPrefix:
+		return func(r io.Reader) {
+			l, _ := coder.DecodeVarInt(r)
+			ioutilx.ReadN(r, int(l))
+		}
+	case urns.CoderVarInt:
+		return func(r io.Reader) {
+			coder.DecodeVarInt(r)
+		}
+	case urns.CoderBool:
+		return func(r io.Reader) {
+			coder.DecodeBool(r)
+		}
+	case urns.CoderDouble:
+		return func(r io.Reader) {
+			coder.DecodeDouble(r)
+		}
+	case urns.CoderIterable:
+		ccids := c.GetComponentCoderIds()
+		ed := pullDecoderNoAlloc(coders[ccids[0]], coders)
+		return func(r io.Reader) {
+			l, _ := coder.DecodeInt32(r)
+			for i := int32(0); i < l; i++ {
+				ed(r)
+			}
+		}
+
+	case urns.CoderKV:
+		ccids := c.GetComponentCoderIds()
+		kd := pullDecoderNoAlloc(coders[ccids[0]], coders)
+		vd := pullDecoderNoAlloc(coders[ccids[1]], coders)
+		return func(r io.Reader) {
+			kd(r)
+			vd(r)
+		}
+	case urns.CoderRow:
+		panic(fmt.Sprintf("Runner forgot to LP this Row Coder. %v", prototext.Format(c)))
+	default:
+		panic(fmt.Sprintf("unknown coder urn key: %v", urn))
+	}
+}