Chapter 294: Bypass Junction

When the taxi pulled up to the side door of the logistics building at the Municipal First Hospital, the pre-dawn wind already carried the chill of dew. Lin Chen paid the fare, pushed the door open, and stepped out. His left foot hit the asphalt, and a sharp pain shot up from his ankle into his calf like a fine needle. He paused for two seconds, shifted his weight to his right leg, and slowly descended the steps. The laptop in his backpack dug into his shoulder blades. He adjusted the strap and headed toward the basement where the Information Technology Department was located.

Most of the motion-sensor lights in the corridor were broken; only the emergency exit sign at the far end cast a faint green glow. Lin Chen scanned his temporary visitor code, pushed open the heavy fire door, and was immediately hit by the low-frequency hum of the server room, mixed with the smell of ozone and dust. Director Liu was already waiting inside, wearing a faded jacket, a bunch of keys in his hand, and red veins in his eyes from a sleepless night.

“Engineer Lin, making a trip out this late.” Director Liu handed him a folding chair and pointed to a dusty server rack in the corner. “That’s the one. The acquisition node for the old PACS. The original vendor’s engineers left a local maintenance port before they pulled out, but the password was lost long ago. We tried resetting it, but we were afraid of corrupting the index database, so we never dared to touch it. All the data the evaluation committee needs is stuck right here.”

Lin Chen nodded without speaking. He set down his backpack, took out his laptop, and connected it to a spare network cable next to the rack. The screen lit up, its cold light reflecting the dark circles under his eyes. He opened a terminal first, ran a basic network scanning tool across the internal subnet, and confirmed the open ports. 8080 and 443 were open, but the handshake protocol returned a SOAP envelope in XML format. A decade-old medical imaging system, forced to adopt this cumbersome standard for compatibility with the HIS of the time. Modern gateways had long since shifted to lightweight RESTful architectures, leaving an invisible wall between them.

“We won’t touch the core database. Just a bypass.” Lin Chen spoke as he rummaged through his bag for a small gigabit switch and two patch cables. He daisy-chained the switch between the acquisition node and the core switch, physically setting up a traffic mirror. The data flow remained unchanged; only a read-only duplicate channel was added.

Director Liu leaned in, frowning. “Will that work? The evaluation committee wants a complete ledger. Won’t packet mirroring miss fields? And if it crashes the old system, the whole hospital’s imaging department shuts down.”

“It won’t miss anything.” Lin Chen’s fingers tapped across the keyboard, bringing up a packet capture tool. “SOAP might be bloated, but its structure is rigid. I’ll intercept the request headers and response bodies, write a parsing layer, and map the XML nodes to JSON. Read-only, no writes, zero impact on your operations. If the connection drops, the switch automatically bypasses, and traffic goes straight through the original path. Zero risk to you.”

He spoke at a measured pace, each word landing like a nail driven into wood. Director Liu listened, didn’t interrupt again, just pulled up a chair and watched the code scroll line by line on the screen. The server room was filled only with the roar of server fans and the occasional click of hard drive read/write heads.

Lin Chen began writing the adaptation script. No ready-made wheels here; he had to build it from scratch. He first defined a base parsing class, used a mature XML processing library to construct a tree structure, and extracted key fields like patient identifiers, examination sequence numbers, and equipment models. For deeply nested nodes, he added recursive traversal. Obscure characters and garbled text were the norm, so he directly applied the fallback logic from his early data-cleaning scripts: unparseable fields were uniformly marked as placeholders, and the hash values of the original byte streams were logged for manual review later. The script wasn’t long, but the logic had to be airtight. Medical data allowed for no luck. A single misplaced comma could invalidate an entire batch of ledgers.

At 2:40 a.m., the first version of the script ran. The terminal window began spitting out logs. At first, red errors flashed: connection refused, timeout. Lin Chen didn’t panic. He checked the handshake parameters line by line and found that the old system’s encryption protocol only supported early TLS 1.0, while the current runtime environment defaulted to rejecting weak encryption. He temporarily adjusted the client’s handshake strategy, suppressing the security warnings. He ran it again.

The progress bar began to crawl forward. Green logs scrolled line by line. Successfully retrieved imaging metadata. Field mapping complete. Output written to local cache.

Lin Chen stared at the screen, his breathing gradually steadying. He opened the generated file and randomly spot-checked a few entries. Timestamps, anonymized IDs, examination sites, equipment models—all aligned perfectly. He turned to Director Liu. “Director Liu, please verify this sample batch. If the fields are correct, I’ll deploy the script to the test environment for a full pull.”

Director Liu leaned closer to the screen, pushed up his glasses, and compared them line by line. After about ten minutes, he straightened up and sighed. “They match. Engineer Lin, your work is truly solid. In the past, when we hired outside contractors, just the integration phase took half a month of wrangling, and what they delivered was full of holes.”

“It’s my job.” Lin Chen closed his laptop and unplugged the patch cables. “I’ll leave a copy of the script on your local drive, set up as a scheduled task to run automatically at 2 a.m. daily. Log files will be archived by date. When the evaluation committee needs to check the ledger, they can just export the spreadsheets. I’ve only left read-only permissions. You can change the password yourself.”

Director Liu took the USB drive and carefully placed it in his drawer. “Alright. Andun’s team will be here tomorrow morning. For the penetration testing side, I’ll have the IT department cooperate and set up a whitelist. You guys hurry up and get it done.”

“Thank you.” Lin Chen stood up. As his left foot touched the floor, another sharp stab of pain shot through it. He braced himself against the edge of the server rack for a few seconds, then slung his backpack over his shoulder.

By the time he walked out of the hospital gates, the sky had already lightened to a pale gray. Early-shift buses were pulling into the station, their exhaust fumes mixing with the smell of oil and smoke from breakfast stalls. Lin Chen sat down on a roadside bench, unscrewed his thermos, and took a gulp of cold, strong tea. His stomach was empty, but he had no appetite. He pulled out his phone and sent a message to Su Man: “PACS bypass is live. Data flow is stable. You can start filling out the ledger template.”

A few seconds later, Su Man replied: “Received. Andun’s initial scan report just came out. There’s an issue.”

Lin Chen’s fingers froze. He opened the file. The report was in PDF format, with a highlighted section reading: “Unauthorized access risk detected on the AI inference interface. Model weight files are not encrypted or isolated. In the internal network test environment, any IP can directly call the core inference service by constructing specific headers. Immediate implementation of API gateway authentication and request rate limiting is recommended.”

He stared at that line, his brows slowly knitting together. Unencrypted model weights. This meant that if someone got hold of the interface address, they could directly call their core algorithms, or even reverse-engineer the distribution characteristics of the training data through high-frequency requests. In a compliance assessment, this was a fatal flaw. Andun’s engineers would be on-site at 9 a.m. tomorrow. If this wasn’t resolved, the penetration test would fail outright, the 35,000 expedited fee would go down the drain, and their evaluation qualification would be revoked along with it.

He leaned back against the bench, closing his eyes. The nine-day countdown had lost another day. No way out. Only forward, filling in the holes. He opened his eyes, created a new line in his notes app: “1. Add JWT authentication middleware 2. Encrypt and store weight files 3. Limit single-IP concurrency threshold 4. Rerun penetration test.”

The wind swept up fallen leaves, brushing against his shoes. Lin Chen slipped his phone back into his pocket and stood up. His left foot still ached, but his stride was steady now. He flagged down a taxi that had just dropped off a passenger and pulled open the door.

“Where to?” the driver asked. “Back to the office,” he said.

The city outside the window was waking up. Lin Chen leaned against the seat, his fingers unconsciously tracing the hard cover of his mistake notebook. He knew the protocol was open, but the door wasn’t fully shut yet. He had to go install the lock.