instances: Add methods to evaluate PHP

internal/component/instances/wisski_php.go

@@ -0,0 +1,122 @@
+package instances
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"strings"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+var ErrExecInvalidCode = errors.New("invalid code to execute")
+var ErrExecNonZero = errors.New("script returned non-zero code")
+
+// ExecPHPScript executes the PHP code as a script within the wisski instance.
+// The script should define a function "main", and may define additional functions.
+//
+// Code must start with "<?php" and may not contain a closing tag.
+// Code is expected not to mess with PHPs output buffer.
+// Code should not contain user input.
+//
+// It's arguments are encoded as json using [json.Marshal] and decoded within php.
+//
+// The return value of the function is again marshaled with json and returned to the caller.
+//
+// Standard input and output streams should not be used.
+// Standard error is redirected to io.
+func (wisski *WissKI) ExecPHPScript(io stream.IOStream, code string, args ...any) (any, error) {
+	// make sure the beginning is right
+	if !strings.HasPrefix(code, "<?php") {
+		return nil, ErrExecInvalidCode
+	}
+
+	// make sure that args is not nil, but an array of length 0!
+	if args == nil {
+		args = []any{}
+	}
+
+	// encode code and args!
+	codeEscape, err := marshalPHP("?>" + code)
+	if err != nil {
+		return nil, err
+	}
+
+	argsEscape, err := marshalPHP(args)
+	if err != nil {
+		return nil, err
+	}
+
+	// assemble the script
+	script := `
+	ob_start(null, 0, PHP_OUTPUT_HANDLER_CLEANABLE);
+	eval(` + codeEscape + `);
+	ob_end_clean();
+
+	call_user_func(function(){
+		ob_start(null, 0, PHP_OUTPUT_HANDLER_CLEANABLE);
+		$result = call_user_func_array("main", ` + argsEscape + `);
+		ob_end_clean();
+		echo json_encode($result);
+	});
+`
+
+	// run the script
+	var output bytes.Buffer
+	res, err := wisski.Shell(io.Streams(&output, nil, strings.NewReader(script), 0), "-c", "drush php:script -")
+	if res != 0 {
+		return nil, ErrExecNonZero
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	// decode the output
+	var result any
+	err = json.NewDecoder(&output).Decode(&result)
+	return result, err
+}
+
+// EvalPHP is similar to ExecPHPScript, except that it evaluates a single line of php.
+// A single parameter may be passed, which can be accessed using the name $arg inside the expression.
+func (wisski *WissKI) EvalPHP(expr string, arg any) (any, error) {
+	return wisski.ExecPHPScript(stream.FromEnv(), "function main($arg){return "+expr+";}", arg)
+}
+
+const marshalRune = 'F' // press to pay respect
+
+// marshalPHP marshals some data which can be marshaled using [json.Encode] into a PHP Expression.
+// the string can be safely used directly within php.
+func marshalPHP(data any) (string, error) {
+	// this function uses json as a data format to transport the data into php.
+	// then we build a heredoc to encode it safely, and decode it in php
+
+	// Step 1: Encode the data as json
+	jbytes, err := json.Marshal(data)
+	if err != nil {
+		return "", err
+	}
+	jstring := string(jbytes)
+
+	// Step 2: Find a delimiter for the heredoc.
+	// Step 2a: Find the longest sequence of [marshalRune]s inside the encoded string.
+	var current, longest int
+	for _, r := range jstring {
+
+		if r == marshalRune {
+			current++
+		} else {
+			current = 0
+		}
+
+		if current > longest {
+			longest = current
+		}
+	}
+	// Step 2b: Build a string of marshalRune that is one longer!
+	delim := strings.Repeat(string(marshalRune), longest+1)
+
+	// Step 3: Assemble the encoded string!
+	result := "call_user_func(function(){$x=<<<'" + delim + "'\n" + jstring + "\n" + delim + ";return json_decode(trim($x));})" // press to doubt
+	return result, nil
+}