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#!/bin/bash

#

# test-config-race.sh - Reproduce config file race condition

#

# This script attempts to reproduce the race condition where:

# 1. Config file is being written (truncated then written)

# 2. Core process starts and reads the partially written file

# 3. Core fails with "invalid character '}'" JSON parse error

#

# Expected result WITHOUT fix: ~5% failure rate (corrupted config reads)

# Expected result WITH atomic writes: 0% failure rate

#

set -e

# Colors for output

RED='\033[0;31m'

GREEN='\033[0;32m'

YELLOW='\033[1;33m'

NC='\033[0m' # No Color

# Configuration

ITERATIONS=${1:-100}

TEST_DIR="/tmp/mcpproxy-race-test-$$"

CONFIG_FILE="$TEST_DIR/mcp_config.json"

RESULTS_FILE="$TEST_DIR/results.txt"

# Counters

SUCCESS_COUNT=0

PARTIAL_READ_COUNT=0

PARSE_ERROR_COUNT=0

echo "=================================================="

echo "Config File Race Condition Reproduction Test"

echo "=================================================="

echo ""

echo "Test directory: $TEST_DIR"

echo "Iterations: $ITERATIONS"

echo ""

# Create test directory

mkdir -p "$TEST_DIR"

# Create a sample config (large enough to have observable write time)

create_large_config() {

local file=$1

cat > "$file" << 'EOF'

{

"listen": "127.0.0.1:8080",

"data_dir": "~/.mcpproxy",

"api_key": "test-api-key-1234567890",

"enable_web_ui": true,

"top_k": 5,

"tools_limit": 15,

"tool_response_limit": 20000,

"mcpServers": [

{

"name": "server-1",

"url": "http://localhost:8001",

"protocol": "http",

"enabled": true,

"quarantined": false

},

{

"name": "server-2",

"url": "http://localhost:8002",

"protocol": "http",

"enabled": true,

"quarantined": false

},

{

"name": "server-3",

"url": "http://localhost:8003",

"protocol": "http",

"enabled": true,

"quarantined": false

},

{

"name": "server-4",

"url": "http://localhost:8004",

"protocol": "http",

"enabled": true,

"quarantined": false

},

{

"name": "server-5",

"url": "http://localhost:8005",

"protocol": "http",

"enabled": true,

"quarantined": false

}

]

}

EOF

}

# Simulate non-atomic write (current implementation)

non_atomic_write() {

local file=$1

local data=$2

# This mimics os.WriteFile behavior: truncate then write

# The file is in a partial state during the write

echo -n "$data" > "$file"

}

# Simulate atomic write (proposed fix)

atomic_write() {

local file=$1

local data=$2

local tmp_file="${file}.tmp.$$"

# Write to temp file

echo -n "$data" > "$tmp_file"

# Fsync (force to disk)

if command -v fsync &> /dev/null; then

fsync "$tmp_file"

elif [[ "$OSTYPE" == "darwin"* ]]; then

# macOS doesn't have fsync command, use sync

sync

fi

# Atomic rename

mv "$tmp_file" "$file"

}

# Reader process that tries to read and parse JSON

read_and_validate() {

local file=$1

local iteration=$2

# Try to read the file

if [ ! -f "$file" ]; then

echo "ITERATION $iteration: File not found" >> "$RESULTS_FILE"

return 1

fi

local content=$(cat "$file")

# Check if content looks incomplete

local char_count=$(echo -n "$content" | wc -c | tr -d ' ')

if [ "$char_count" -lt 100 ]; then

echo "ITERATION $iteration: PARTIAL READ (only $char_count chars)" >> "$RESULTS_FILE"

echo "$content" >> "$RESULTS_FILE"

echo "---" >> "$RESULTS_FILE"

return 2

fi

# Try to parse as JSON

if ! echo "$content" | jq . > /dev/null 2>&1; then

echo "ITERATION $iteration: JSON PARSE ERROR" >> "$RESULTS_FILE"

echo "$content" >> "$RESULTS_FILE"

echo "---" >> "$RESULTS_FILE"

return 3

fi

echo "ITERATION $iteration: SUCCESS" >> "$RESULTS_FILE"

return 0

}

# Test function

run_test() {

local use_atomic=$1

local iteration=$2

# Generate new config content

local config_content

config_content=$(cat << EOF

{

"listen": "127.0.0.1:8080",

"data_dir": "~/.mcpproxy",

"api_key": "test-key-iteration-$iteration",

"enable_web_ui": true,

"top_k": 5,

"tools_limit": 15,

"tool_response_limit": 20000,

"mcpServers": [

{"name": "server-$iteration-1", "url": "http://localhost:8001", "enabled": true},

{"name": "server-$iteration-2", "url": "http://localhost:8002", "enabled": true},

{"name": "server-$iteration-3", "url": "http://localhost:8003", "enabled": true},

{"name": "server-$iteration-4", "url": "http://localhost:8004", "enabled": true},

{"name": "server-$iteration-5", "url": "http://localhost:8005", "enabled": true}

]

}

EOF

)

# Start writer in background

if [ "$use_atomic" = "true" ]; then

atomic_write "$CONFIG_FILE" "$config_content" &

else

non_atomic_write "$CONFIG_FILE" "$config_content" &

fi

local writer_pid=$!

# Immediately try to read (race condition)

# Add tiny delay to simulate core startup time

sleep 0.001

read_and_validate "$CONFIG_FILE" "$iteration"

local result=$?

# Wait for writer to finish

wait $writer_pid 2>/dev/null || true

return $result

}

# Run tests with NON-ATOMIC writes

echo "Running test with NON-ATOMIC writes (current implementation)..."

echo "This should show race condition failures (~5% of the time)"

echo ""

> "$RESULTS_FILE"

for i in $(seq 1 $ITERATIONS); do

if [ $((i % 10)) -eq 0 ]; then

echo -n "."

fi

run_test "false" "$i"

result=$?

case $result in

0) ((SUCCESS_COUNT++)) ;;

2) ((PARTIAL_READ_COUNT++)) ;;

3) ((PARSE_ERROR_COUNT++)) ;;

esac

done

echo ""

echo ""

echo "=================================================="

echo "Results (NON-ATOMIC writes):"

echo "=================================================="

echo -e "${GREEN}Successful reads: $SUCCESS_COUNT / $ITERATIONS${NC}"

echo -e "${YELLOW}Partial reads: $PARTIAL_READ_COUNT / $ITERATIONS${NC}"

echo -e "${RED}Parse errors: $PARSE_ERROR_COUNT / $ITERATIONS${NC}"

echo ""

TOTAL_FAILURES=$((PARTIAL_READ_COUNT + PARSE_ERROR_COUNT))

FAILURE_RATE=$((TOTAL_FAILURES * 100 / ITERATIONS))

if [ $TOTAL_FAILURES -gt 0 ]; then

echo -e "${RED}⚠️ RACE CONDITION DETECTED!${NC}"

echo -e "${RED} Failure rate: ${FAILURE_RATE}% ($TOTAL_FAILURES failures in $ITERATIONS attempts)${NC}"

echo ""

echo "Sample failures saved to: $RESULTS_FILE"

echo ""

echo "First 3 failures:"

grep -A 5 "PARTIAL READ\|PARSE ERROR" "$RESULTS_FILE" | head -n 20

else

echo -e "${GREEN}✓ No race condition detected${NC}"

echo " (Note: Race conditions are probabilistic - try increasing iterations)"

fi

echo ""

echo "=================================================="

# Now test with ATOMIC writes

echo ""

echo "Running test with ATOMIC writes (proposed fix)..."

echo "This should show NO failures"

echo ""

SUCCESS_COUNT=0

PARTIAL_READ_COUNT=0

PARSE_ERROR_COUNT=0

> "$RESULTS_FILE"

for i in $(seq 1 $ITERATIONS); do

if [ $((i % 10)) -eq 0 ]; then

echo -n "."

fi

run_test "true" "$i"

result=$?

case $result in

0) ((SUCCESS_COUNT++)) ;;

2) ((PARTIAL_READ_COUNT++)) ;;

3) ((PARSE_ERROR_COUNT++)) ;;

esac

done

echo ""

echo ""

echo "=================================================="

echo "Results (ATOMIC writes):"

echo "=================================================="

echo -e "${GREEN}Successful reads: $SUCCESS_COUNT / $ITERATIONS${NC}"

echo -e "${YELLOW}Partial reads: $PARTIAL_READ_COUNT / $ITERATIONS${NC}"

echo -e "${RED}Parse errors: $PARSE_ERROR_COUNT / $ITERATIONS${NC}"

echo ""

TOTAL_FAILURES=$((PARTIAL_READ_COUNT + PARSE_ERROR_COUNT))

if [ $TOTAL_FAILURES -gt 0 ]; then

echo -e "${RED}⚠️ UNEXPECTED FAILURES WITH ATOMIC WRITES!${NC}"

echo -e "${RED} This should not happen - atomic writes should prevent all race conditions${NC}"

exit 1

else

echo -e "${GREEN}✓ No race condition detected with atomic writes${NC}"

echo -e "${GREEN}✓ All $ITERATIONS reads were successful${NC}"

fi

echo ""

echo "=================================================="

echo "Test complete!"

echo "=================================================="

# Cleanup

rm -rf "$TEST_DIR"

echo ""

echo "Summary:"

echo " - Non-atomic writes are susceptible to race conditions"

echo " - Atomic writes (temp + rename) prevent all race conditions"

echo " - This reproduces the issue reported in GitHub issue #86"