Offer unlimited log buffer size when scanning handler logs

[alexellis]

Description

Offer unlimited log buffer size when scanning handler logs

Motivation and Context

Some users have complained that they cannot log lines longer than 16KB. A 16KB log line seems excessive, but this has been requested at least 2-3 times over the years. For example: #100

To enable the feature, set log_buffer_size to -1. This is not a default, because it is not as efficient as using a pre- determined buffer size.

How Has This Been Tested?

Tested by running curl with --data-binary and sending a 6.7M Go binary into a function with the 16KB maximum log line size set. That produced the error, when the size was set to -1, the output was written, albeit quite slowly.

The error before the changes:

Sample function which prints any input HTTP body to stderr

package function

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
)

type Res struct {
	Body string `json:"body"`
}

func Handle(w http.ResponseWriter, r *http.Request) {
	var input []byte

	if r.Body != nil {
		defer r.Body.Close()

		body, _ := io.ReadAll(r.Body)

		input = body
	}

	jres, err := json.Marshal(Res{Body: string(input)})
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	log.Printf("%s", string(jres))

	w.WriteHeader(http.StatusOK)
	w.Write([]byte(fmt.Sprintf("Body: %s", string(input))))
}

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.